Numbers implying algebraic structures
A Plonka sum of algebras is called proper if the semilattice-ordered system for the sum is not trivial and the algebras involved in the sum are not all trivial. The main result of the paper: A commutative idempotent groupoid is a proper Plonka sum of affine spaces over GF(3) if and only if it has 27 essentially 4-ary term functions.
scientific article; zbMATH DE number 1383741