In fact, there are many counterexamples. Here is a simple example:

The definition domain of f is set to p, and the range is set to q; The definition domain of g and h is set to q, and the value domain is set to r.

Let p have elements {a, b}, q have elements {c, d}, and r have elements {e, f}.

Order f: a-> CB-> C.

g:c->e d->e

h:c->e d->f

Where-> Indicates that the mapping meets the condition.

If you don't understand, you can ask.