Description: A walk of length N as word corresponds to the sequence of vertices
in a walk of length N in a pseudograph. This variant of
wlklnwwlkln2 does not require G to be a simple pseudograph, but it
requires (indirectly) the Axiom of Choice. (Contributed by Alexander
van der Vekens, 21-Jul-2018)(Revised by AV, 12-Apr-2021)