A simple proof of the exactness of expanding maps of the interval with an indifferent fixed point

Abstract: Expanding maps with indifferent fixed points, a.k.a. intermittent maps, are popular models in nonlinear dynamics and infinite ergodic theory. We present a simple proof of the exactness of a wide class of expanding maps of [0,1], with countably many surjective branches and a strongly neutral fixed point in 0.