Gumm terms

Summary

Gumm terms are a finite chain of ternary terms of a variety. They combine a chain like Jónsson terms with a final step like a Mal'cev term. A variety has Gumm terms if and only if it is a congruence-modular variety. This form of the Mal'cev condition for modularity shows that congruence modularity mixes the two basic cases, congruence distributivity and congruence permutability.