  Congruence modular and congruence distributive varieties can be characterized
by the existence of sequences of Gumm and J\'onsson terms, respectively. Such
sequences have variable lengths, in general. It is immediate from the above
paragraph that there is a variety with Gumm terms but without J\'onsson terms.
We prove the quite unexpected result that, on the other hand, if some variety
has both kinds of terms, then the minimal lengths of the sequences differ at
most by $1$. It follows that every $r$-modular congruence distributive variety
is $r^2-r+2$-distributive.

Rings and Algebras