  In this paper, the concordance of Morse functions is defined, and a necessary
and sufficient condition for given two Morse functions to be concordant is
presented and is compared with the cobordism criterion. Cobordism of Morse
functions on smooth closed manifolds is an equivalence relation defined by
using cobordisms of manifolds and fold maps. Given two Morse functions, it is
important to decide whether they are cobordant or not, and this problem was
first solved for surfaces and then for manifolds of general dimensions by
Ikegami-Saeki, Kalm\'ar, and Ikegami. On the other hand, for Morse functions on
the same manifold, we can consider a stronger equivalence relation called
concordance.
