Tether: Autonomous Functional Play with Correspondence-Driven Trajectory Warping
Abstract: The ability to conduct and learn from interaction and experience is a central challenge in robotics, offering a scalable alternative to labor-intensive human demonstrations. However, realizing such "play" requires (1) a policy robust to diverse, potentially out-of-distribution environment states, and (2) a procedure that continuously produces useful robot experience. To address these challenges, we introduce Tether, a method for autonomous functional play involving structured, task-directed interactions. First, we design a novel open-loop policy that warps actions from a small set of source demonstrations (<=10) by anchoring them to semantic keypoint correspondences in the target scene. We show that this design is extremely data-efficient and robust even under significant spatial and semantic variations. Second, we deploy this policy for autonomous functional play in the real world via a continuous cycle of task selection, execution, evaluation, and improvement, guided by the visual understanding capabilities of vision-LLMs. This procedure generates diverse, high-quality datasets with minimal human intervention. In a household-like multi-object setup, our method is the first to perform many hours of autonomous multi-task play in the real world starting from only a handful of demonstrations. This produces a stream of data that consistently improves the performance of closed-loop imitation policies over time, ultimately yielding over 1000 expert-level trajectories and training policies competitive with those learned from human-collected demonstrations.
Paper Prompts
Sign up for free to create and run prompts on this paper using GPT-5.
Top Community Prompts
Explain it Like I'm 14
What is this paper about?
This paper is about teaching a robot to learn new skills by “playing” on its own, instead of relying on lots of human teaching. The authors introduce a system called Tether that:
- Uses just a few example demonstrations (10 or fewer) to figure out how to act in new situations.
- Lets the robot run for many hours, choosing tasks, trying them, checking if it succeeded, and getting better over time with very little human help.
What questions did the researchers ask?
The paper focuses on two simple questions:
- How can a robot copy a skill from just a handful of examples and still work when the scene looks different (objects moved, different objects, clutter)?
- How can a robot collect useful practice data by itself for many hours, so later it can learn even better “closed-loop” skills (skills that adjust as they go)?
How did they do it?
Learning from a few examples
Instead of training a huge neural network that needs tons of data, Tether starts with just a small set of human demonstrations for each task (like “put the pineapple in the bowl”). Each demo records:
- A short list of important “waypoints” in 3D that the robot’s hand (gripper) visits, like “above bowl,” “inside bowl,” “back to start.”
- The full action sequence between those waypoints (the exact path the hand took).
- Two camera images of the scene at the start.
Matching key points like stickers
Imagine you put tiny sticker dots on the important spots in a demo image (for example, the center of the pineapple or the rim of the bowl). When the robot sees a new scene, it uses modern computer vision to find the matching spots—like finding where those “stickers” would be now, even if the bowl moved or it’s a different bowl.
These “keypoint correspondences” tell the robot where the important places are in the new scene.
Warping the moves to fit the new scene
“Warping” here means bending and shifting the recorded motion so it fits the new object positions.
- The robot picks the demo whose keypoints best match the current scene.
- It computes how much each important waypoint moved from the old scene to the new one.
- Then it smoothly shifts the entire action path between waypoints by the same amounts, like tracing a drawing and sliding parts of the trace so it lines up with a moved picture.
This is called “open-loop” execution: the robot plans the whole motion and runs it, without constantly checking and correcting in the middle.
A simple analogy:
- Open-loop is like following a recipe step-by-step without tasting.
- Closed-loop is like tasting as you cook and adjusting salt and heat. Tether starts open-loop to get lots of practice data, then later trains closed-loop policies.
Letting the robot “play” by itself
To scale up practice without humans:
- Task selection: A vision-LLM (VLM)—an AI that understands pictures and text—looks at the scene and suggests which task to try next (for example, “move the bowl to the shelf”). Tasks are chosen so one task’s ending sets up another task’s start, creating natural “resets” without a person stepping in.
- Execution: The Tether policy runs the warped trajectory for that task.
- Success checking: The VLM looks at before-and-after images and judges if the task succeeded.
- Improvement: The system also learns which source demos are most reliable to warp from, using a “try-and-trust” strategy (a multi-armed bandit with UCB). Think of it as trying different teachers, favoring the ones that work best, but still occasionally testing others.
Training better skills from the play data
As the robot collects many successful attempts, those recordings are used to train stronger “closed-loop” neural policies that do adjust mid-action. Over time, these policies get better and more reliable.
What did they find?
Here are the main results and why they matter:
- Strong performance from very few demos:
- Across 12 household-like tasks, Tether worked well even with just 10 demonstrations per task.
- It beat several modern baselines that either needed more data or struggled in complex scenes.
- Robust to changes in position and even object type:
- It handled objects placed in new spots.
- It also worked with different objects than the demos (for example, swapping a pineapple for an apple or a strawberry, and a bowl for a basket or a cup), thanks to smart keypoint matching that finds “the same part” of a new object.
- Handles tricky manipulation:
- Tasks included wiping a whiteboard with a cloth (deformable), opening a tight cabinet door (articulated), hanging tape on a small hook (tiny target), and inserting a coffee pod with only about 8 mm of wiggle room (high precision).
- Long, mostly hands-free play:
- The robot ran around 26 hours of autonomous play, producing over 1,000 successful trajectories with only 5 brief human interventions (about 0.26% of attempts).
- The VLM planner and success checker were accurate and reliable.
- Data that makes future learning better:
- Using the collected successes, the team trained closed-loop policies that improved steadily and reached high success rates.
- These policies became competitive with policies trained on similar numbers of human-collected demonstrations.
- Importantly, when tested on the messy, real “states” created by free-form play (tilted objects, odd placements), Tether’s approach was more reliable than a standard learned policy trained on many human demonstrations, showing it’s especially good at coping with weird situations.
Why does this matter?
- Less human effort: Robots can improve by practicing on their own, reducing the need for lots of human demonstrations.
- Works in the real world: The system runs for many hours in a real, cluttered environment and creates high-quality training data.
- Generalizes well: Matching key “parts” of scenes makes it robust to object changes and new layouts.
- Builds a path to smarter robots: Tether kick-starts learning with a powerful, low-data open-loop method, then uses the collected data to train stronger closed-loop skills.
Limits and future directions:
- Open-loop plans can’t react to surprises mid-motion and can struggle with occlusions (when important parts are hidden).
- Some complex motions can’t be neatly “warped” from demos.
- A promising next step is to combine Tether’s strong start (few demos, great generalization) with closed-loop learning and reinforcement learning so the robot keeps getting smarter as it plays.
Knowledge Gaps
Knowledge gaps, limitations, and open questions
Below is a concise list of concrete gaps and open questions left unresolved by the paper. Each point is framed to help guide specific follow-up research.
- Open-loop execution limits: How to extend the warping policy to closed-loop control that can react to slippage, perturbations, or misalignment mid-trajectory without relying on post-hoc VLM evaluation.
- Occlusion susceptibility: The approach assumes minimal occlusion and full observability from fixed third-person cameras; robustness under heavy occlusion, self-occlusion, or partial observability (e.g., only a wrist cam) is not evaluated.
- Dependence on camera calibration and fixed viewpoints: Sensitivity to calibration errors, camera drift, or moving sensors (e.g., mobile base, pan-tilt cameras) is unstudied; how to make correspondence and backprojection robust or self-calibrating remains open.
- Orientation and SE(3) warping: The warping method is defined primarily on 3D positions with linear displacement interpolation; a principled, general SE(3) trajectory warp (including orientation, velocity profiles, and timing) is not described or analyzed.
- Complex non-linear motion constraints: The method assumes trajectories can be linearly warped between waypoint displacements; how to handle non-linear path constraints (e.g., around obstacles), non-isometric deformations, or topology changes is unaddressed.
- Force/torque and compliance: Execution ignores force profiles and haptics; how to incorporate force sensing, impedance control, or contact-rich feedback during warping (e.g., for insertion, sliding, scrubbing) is not explored.
- Dynamic or moving objects: The approach targets largely static scenes; applicability to tasks with moving objects, humans, or time-varying goals is not studied.
- Failure detection and online recovery: There is no mechanism to detect and correct miswarps or early failures during execution; designing “abort-and-replan” or self-correction strategies remains open.
- Generalization breadth of semantic correspondences: While a few out-of-distribution objects are tested (apple, strawberry, basket, cup), systematic evaluation across categories, materials (transparent/reflective), sizes, textures, and clutter levels is missing.
- Robustness of correspondence models: The system relies on a specific correspondence backbone (DINOv2 + Stable Diffusion features). Sensitivity to the choice of matcher, lighting changes, domain shifts, or distractors is not quantified.
- Multi-object and cluttered scenes: Scalability to many simultaneously relevant objects and heavy clutter (including stacked, partially hidden, or similarly colored items) remains untested.
- Waypoint selection strategy: Waypoints are defined by gripper open/close toggles; whether learning task-specific or automatically discovered waypoints improves robustness and generality is not investigated.
- Long-horizon and hierarchical tasks: VLM planning executes only the first step of a plan per iteration; how to execute longer sequences robustly (multi-step with interdependent subgoals) and prevent drift over long horizons is open.
- Reset-free play beyond composable tasks: The approach depends on task sets that naturally reset or compose; how to generalize reset-free play to tasks without natural reversibility or with hard-to-recover states is unclear.
- Irrecoverable states and autonomous recovery: The system needed occasional human interventions (e.g., bowl flipped upside down). Methods for autonomous recovery from such states (e.g., multi-step manipulation, exploration policies) are not developed.
- Data efficiency vs. diversity trade-offs: The method filters to successful trajectories for training; leveraging failures or near-misses (via offline RL, inverse RL, preference learning, or relabeling) to improve efficiency is not explored.
- Dataset bias and distributional drift during play: As play broadens the state distribution, how to monitor and control drift (to preserve safety and maintainability) or to adapt policies or curricula accordingly is unspecified.
- Safety and collision handling: The paper does not detail safety constraints, collision monitoring, or risk-sensitive planning during open-loop warps; formalizing and enforcing safety during autonomous play remains an open problem.
- Throughput and latency analysis of VLM components: The computational cost, latency, and reliability of VLM task selection and success evaluation under different models and hardware are not systematically measured or optimized.
- Generalization across platforms: Validation is on a single Franka arm in one environment; transfer to different robots (kinematics, grippers), bimanual setups, mobile manipulation, or varied environments is not shown.
- Scaling to multi-robot fleets: How to coordinate autonomous play, share data, and schedule tasks across multiple robots to accelerate dataset growth is unaddressed.
- Formal guarantees and error bounds: There is no analysis of conditions under which trajectory warping remains valid, nor error bounds relating keypoint matching error to end-effector pose and task success probability.
- Sensitivity to number/quality of demos: While a bandit selects “better” source demos, the method’s sensitivity to k, demo quality/noise, and demo diversity (coverage) is not characterized; principled demo curation remains open.
- Orientation-critical tasks at a distance: For very small features (e.g., 2–3 px at standard views), the paper resorts to moving cameras closer; strategies for scale-invariant correspondence, adaptive zooming, or active viewpoint control are not developed.
- Alternatives to linear interpolation in space: The choice to interpolate displacements in the local line segment space is heuristic; exploring spline-based warping, geodesic interpolation on manifolds, or learned warp fields could improve fidelity.
- Handling reflective/transparent or deformable targets: Keypoint matching on reflective or transparent objects (glass, metal) and highly deformable targets (cloth beyond grasp point, cables, bags) is not extensively evaluated.
- Using wrist or tactile sensing for correspondence: The policy and correspondence use only third-person RGB; integrating wrist camera, depth, or tactile cues to improve matching and reduce occlusion sensitivity is unexplored.
- Learning to predict correspondence uncertainty: The system treats correspondences deterministically; estimating per-keypoint uncertainty to weight warps or reject unreliable matches is a potential improvement not examined.
- Task planning with VLMs under ambiguity: Although planning accuracy is high in this setup, robustness to ambiguous scenes, out-of-vocabulary objects, or adversarial distractors (and fallback strategies) is not studied.
- Cost-aware selection of tasks and demos: The bandit balances demo success but not execution cost/risk; integrating cost, safety, and novelty into the selection objective is not addressed.
- Benchmarking against broader baselines: Comparisons exclude other correspondence/warp methods, closed-loop classical controllers using pose estimation, or hybrid methods; broader benchmarking would clarify where Tether is most advantageous.
- Reproducibility with open VLMs: The success evaluation uses a proprietary VLM (Gemini Robotics-ER 1.5); how performance transfers to open-source alternatives and under different prompt designs remains open.
- Code/data release and standardized evaluation: The paper does not state whether datasets and code will be released, nor propose standardized play benchmarks for fair comparison across methods.
- Integration with RL for self-improvement: While suggested in limitations, concrete methods for using Tether as a prior for RL (e.g., warm-start policies, reward shaping from correspondences) are not developed or evaluated.
Practical Applications
Immediate Applications
The following use cases can be deployed now with moderate engineering effort, leveraging the paper’s correspondence-driven trajectory warping, VLM-guided task planning, and success evaluation. Each item notes key sectors, potential tools/workflows, and assumptions that impact feasibility.
- Autonomous generation of expert-level robot demonstrations
- Sectors: robotics R&D, software/tools, manufacturing pilot cells, warehousing, service/home robotics
- Tools/workflows: “Autonomous Play Orchestrator” that cycles task selection (VLM), execution (trajectory warping), and success filtering; dataset curation pipelines for filtered behavioral cloning
- Assumptions/dependencies: two well-placed, calibrated RGB cameras with sufficient visibility; reliable keypoint correspondence models (e.g., DINOv2-based); access to a capable VLM for planning and success detection; relatively static scenes and non-adversarial occlusions
- Few-shot task deployment for pick-place, cabinet opening, and surface wiping
- Sectors: facilities management, hospitality, retail backrooms, labs, home robotics
- Tools/workflows: “Teach-by-Example” modules that warp from ≤10 demos to new object instances/poses; prebuilt task templates (place item X into container Y; open door/cabinet; wipe surface)
- Assumptions/dependencies: tasks are largely quasi-static; gripper and workspace safety limits suitable for open-loop execution; correspondence remains reliable on target objects (including OOD but semantically similar instances)
- Rapid prototyping and retargeting of manipulation skills across similar stations
- Sectors: SME manufacturing (high-mix/low-volume), lab automation, R&D testbeds
- Tools/workflows: trajectory-warping SDKs for ROS/industrial controllers; “retarget to new fixture” utilities that backproject keypoints and generate waypoint-adjusted action plans
- Assumptions/dependencies: accurate camera extrinsics to backproject 2D matches to 3D; limited need for reactive recovery; safe clearances for open-loop insertion/placement
- Automated success/failure labeling for robotic datasets
- Sectors: robotics software, MLOps for embodied AI, QA of assembly cells
- Tools/workflows: VLM-based success evaluators using pre/post multiview images; integration into CI pipelines for robot policy training and monitoring
- Assumptions/dependencies: high-precision VLM judgments (multi-view input significantly boosts precision); guardrails against false positives (e.g., human-in-the-loop verification thresholds)
- Reset-free experimental data collection in labs and classrooms
- Sectors: academia, education, corporate research labs
- Tools/workflows: composable task sets that naturally induce resets; UCB-based demo selection for exploration/exploitation; “play sessions” that produce diverse trajectories for class projects
- Assumptions/dependencies: tasks designed to be composable so end states feed subsequent tasks; minimal human interventions for rare irrecoverable states
- Benchmarking and stress-testing of generalization
- Sectors: robotics benchmarking consortia, internal QA teams
- Tools/workflows: use correspondence-driven warping to systematically vary object instances and placements, evaluating spatial/semantic robustness of existing controllers
- Assumptions/dependencies: consistent camera coverage; standardized object sets and placement distributions
- Demo triage and curation using bandit-based source selection
- Sectors: robotics data ops, teleoperation teams
- Tools/workflows: multi-armed bandit (UCB) to surface high-quality demos for warping, identify brittle demonstrations (e.g., fingertip grasps), and prioritize re-collection
- Assumptions/dependencies: sufficient play throughput to estimate demo quality; success detection precision remains high
Long-Term Applications
These use cases require further research or integration (e.g., closed-loop control, richer sensing, occlusion handling, safety/regulatory frameworks), but are directionally enabled by the paper’s findings.
- Self-improving home and enterprise robots via autonomous functional play
- Sectors: home robotics, office/facilities, hospitality
- Tools/workflows: continuous “play → filter → train → deploy” loops; closed-loop policies trained on growing play datasets; on-device or edge-cloud training
- Assumptions/dependencies: robust safety monitors, collision avoidance, and human-aware policies; improved correspondence under occlusions; integration with wrist/depth/tactile sensing; reliable long-horizon task planning
- Fleet-scale “data flywheels” for generalist robot policies
- Sectors: robotics platforms, cloud robotics providers
- Tools/workflows: centralized platforms aggregating autonomous play data from fleets; standardized VLM-based evaluators; cross-site replay and distilled model updates
- Assumptions/dependencies: privacy/security and data governance; cross-robot calibration and station variability; cost-effective inference and storage
- Agile manufacturing for high-mix/low-volume production
- Sectors: manufacturing, electronics assembly, contract manufacturing
- Tools/workflows: few-shot station bring-up using trajectory warping; automatic generation of expert trajectories for each new SKU; fine-tuning closed-loop policies on curated play data
- Assumptions/dependencies: safety-certified controllers; tighter tolerances handled by closed-loop controllers or learned residuals; integration with industrial cameras and PLCs
- Warehouse and retail restocking in semi-structured environments
- Sectors: logistics, retail operations
- Tools/workflows: restock and re-slotting tasks that adapt from a handful of demonstrations; autonomous resets via composable task graphs across zones
- Assumptions/dependencies: mobile manipulation and navigation stacks; robust perception under clutter and occlusion; SKU variability and packaging constraints
- Assistive and healthcare-adjacent manipulation
- Sectors: eldercare, rehabilitation support, hospital logistics
- Tools/workflows: generalized pick-place and organization from few examples (e.g., transferring supplies, opening cabinets); incremental self-improvement in controlled wards
- Assumptions/dependencies: strict safety and compliance; human-in-the-loop oversight; sterile and unpredictable environments require reactive, closed-loop policies and richer sensing
- Precise insertion and tool-use tasks with hybrid control
- Sectors: advanced assembly, lab automation
- Tools/workflows: combine trajectory warping for coarse placement with learned closed-loop or force/tactile residuals for fine insertion; automated collection of rare, high-precision successes
- Assumptions/dependencies: tactile/force sensing and high-frequency control; failure recovery strategies; accurate calibration and environmental stability
- Policy and standards for autonomous self-improving robots
- Sectors: public policy, safety certification bodies, enterprise risk management
- Tools/workflows: guidelines for autonomous data generation (precision/recall targets for success detectors, human-intervention thresholds, task composability requirements); audit trails for self-generated datasets
- Assumptions/dependencies: consensus on risk categories and acceptable autonomy levels; standardized metrics and reporting for play-based systems
- Commercial “Autonomous Play Platform” as a product
- Sectors: robotics software vendors, system integrators
- Tools/workflows: packaged stack including (1) keypoint-correspondence trajectory warping, (2) VLM-based planning and evaluation, (3) bandit demo selection, (4) dataset management and filtered BC training, with connectors for common robot arms and sensors
- Assumptions/dependencies: licensing and performance of foundation models; device support (UR/Franka/etc.); service SLAs and safety features
- Bridging sim-to-real with real-world play data
- Sectors: simulation toolchains, foundation-model training
- Tools/workflows: use Tether to seed real, diverse trajectories that close the sim-to-real gap for contact-rich tasks; co-training with synthetic data
- Assumptions/dependencies: scalable pipelines for synchronization between sim and real; robust domain randomization and rendering; consistent object geometry and materials metadata
- Education-at-scale using self-generating datasets
- Sectors: higher education, online robotics programs
- Tools/workflows: remote labs where robots autonomously produce datasets for coursework; student evaluation on policy improvement over play iterations
- Assumptions/dependencies: safe unattended operation; scheduling and sandboxing of student tasks; monitoring and auto-recovery from irrecoverable states
Glossary
- 6-DOF: Six degrees of freedom describing a rigid body's position and orientation in 3D space. "The actions at are the 6-DOF pose of robot gripper and the gripper's binary open/close command."
- action affordances: Action possibilities offered by objects or environments, often used as priors for manipulation. "These works build action affordances or primitives (Kuang et al., 2024; Haldar & Pinto, 2025)"
- autonomous functional play: Structured, task-directed robot interactions performed without human intervention to generate learning experience. "we introduce Tether, a method for autonomous functional play involving structured, task-directed interactions."
- backprojection: Mapping image points back into 3D space using camera calibration to recover spatial positions. "If the backprojections fail to intersect, then the match is deemed to have failed"
- calibrated camera extrinsics: Camera parameters describing pose relative to the world, used to transform between image and 3D coordinates. "We then backproject these correspondences K¿ using calibrated camera extrinsics to obtain a sequence of target 3-D waypoints W ¿."
- closed-loop imitation policies: Imitation policies that use ongoing sensory feedback during execution to adjust actions. "This produces a stream of data that consistently improves the performance of closed-loop imitation policies over time"
- Controlled Markov Process (CMP): A formal control model defined by states, actions, and transition dynamics. "We formulate robot manipulation as a Controlled Markov Process (CMP)."
- diffusion policy: A visuomotor policy learned via diffusion models to generate action sequences from observations. "Diffusion Policy (DP) (Chi et al., 2023) is a general imitation learning algorithm"
- filtered behavioral cloning: Training an imitation policy using only trajectories filtered as successful or high-quality. "we adopt filtered behavioral cloning as a straightforward and effective approach."
- foundation models: Large-scale pretrained models used as general-purpose backbones for downstream tasks. "many prior efforts turn to scaling data and policy architectures, often with foundation models or large human-collected demo datasets"
- in-context learning: A model’s ability to infer and apply task patterns from demonstrations at inference time without parameter updates. "it struggled with in-context learning from the complex multi-dimensional patterns in our tasks"
- keypoint correspondences: Matched visual points across images identifying semantically equivalent parts or locations. "Another class instead uses keypoint correspondences as a compact trajectory representation."
- multi-arm bandit: A sequential decision framework balancing exploration and exploitation when choosing among uncertain options. "we select the top k demos by formulating a multi-arm bandit problem"
- non-parametric: Methods that do not learn a fixed parameterized function; they operate by using stored data at inference. "Our policy is non-parametric, and relies on accessing demonstrations at test time."
- object-centric: Approaches centered on per-object representations and reasoning rather than global scene-level modeling. "Like object-centric approaches (Devin et al., 2018; Qian et al., 2024; Zhao et al., 2025)"
- open-loop policy: A policy that plans and executes an action sequence without feedback-driven adjustments during execution. "we design a novel open-loop policy that warps actions from a small set of source demonstrations (≤ 10)"
- out-of-distribution: States or inputs that differ significantly from those seen during training, challenging generalization. "robust to diverse, potentially out-of-distribution environment states"
- point-conditioned policies: Policies that take specified 2D/3D points (e.g., keypoints) as inputs to condition action generation. "P3-PO (Levy et al., 2024) and SKIL (Wang et al., 2025) input keypoints to point-conditioned policies."
- receding horizon control: Planning over a short horizon and executing only the first action before replanning iteratively. "similar to receding horizon control."
- semantic image keypoint correspondences: Keypoint matches based on semantic features that identify equivalent parts across different scenes and objects. "our architecture exploits the remarkable leaps in semantic image keypoint correspondences"
- sim-to-real transfer: The process of transferring policies or models trained in simulation to perform effectively in the real world. "simulation-based approaches struggle with sim-to-real transfer within cluttered, unstructured environments"
- teleoperated demonstrations: Human-controlled robot demonstrations recorded to serve as expert trajectories for training. "trained on real-world teleoperated demonstrations."
- trajectory warping: Transforming a demonstrated motion trajectory to fit a new scene using computed correspondences and displacements. "we show in Section 4.2 that our correspondence-driven trajectory warping performs remarkably well"
- upper confidence bounds: A bandit algorithm that selects actions with the highest upper confidence estimate to balance exploration and exploitation. "For this problem, we use upper confidence bounds (Garivier & Moulines, 2011)"
- vision-language-action models (VLAs): Models that jointly process visual and textual inputs to output action commands for embodied control. "and finetuning vision-language-action models (VLAs) (Black et al., 2024; NVIDIA et al., 2025; Intelligence et al., 2025)."
- vision-LLM (VLM): Models that jointly understand images and text for tasks like planning and evaluation in robotics. "we query a vision-LLM (VLM) to repeatedly plan and select tasks our policy should attempt."
- waypoints: Key intermediate 3D positions used to summarize and guide motion trajectories. "W is a 'waypoint' sequence [w1, w2, ... , WT] of task-critical 3-D gripper locations."
- zero-shot: Performing a task without any finetuning or additional task-specific training. "Meanwhile, zero-shot To performs well on standard tabletop pick-and-place"
Collections
Sign up for free to add this paper to one or more collections.