Picture-valued biquandle bracket

Abstract: In [14], the second named author constructed the bracket invariant [.] of virtual knots valued in pictures (linear combinations of virtual knot diagrams with some crossing information omitted), such that for many diagrams K, the following formula holds: [K]=K', where K' is the underlying graph of the diagram, i.e., the value of the invariant on a diagram equals the diagram itself with some crossing information omitted. This phenomenon allows one to reduce many questions about virtual knots to questions about their diagrams. In [25], the authors discovered the following phenomenon: having a biquandle colouring of a certain knot, one can enhance various state-sum invariants (say, Kauffman bracket) by using various coefficients depending on colours. Taking into account that the parity can be treated in terms of biquandles, we bring together the two ideas from these papers and construct the the picture-valued parity biquandle bracket for classical and virtual knots. This is an invariant of virtual knots valued in pictures. Both the parity bracket and Nelson-Orrison-Rivera invariants are partial cases of this invariants, hence this invariant enjoys many properties of various kinds.