Exchange symmetries in Motzkin path and bargraph models of copolymer adsorption (Q1348849)

This paper derives generating functions for various versions of the problem of random walks in a plane when the walk is never allowed to drop below a fixed line and backward steps are not allowed. Also the vertices or edges of the walk may be coloured. The method used is described is an ``exchange'' method in which the generating function is divided up into a sum over various possible ways in which a walk can start. Explicit formulae for the generating functions and critical activities are given for several models. 20 references. Reviewer's note: This technique seems to be new and useful, and capable of further development.