  We consider the problem of extending partial edge colorings of (iterated)
cartesian products of even cycles and paths, focusing on the case when the
precolored edges constitute a matching. We prove the conjecture of Casselgren,
Granholm and Petros that a precolored distance 3 matching in the Cartesian
product of two even cycles can be extended to a 4-coloring of the edge set of
the whole graph. Actually, a generalization for the Cartesian product of two
bipartite graphs is proved.
