Scrabble?! DIFUNCTIONAL

Definitions of DIFUNCTIONAL in various dictionaries:

In mathematics, a heterogeneous relation is a subset of a Cartesian product A × B, where A and B are distinct sets. A heterogeneous relation has been called a rectangular relation, suggesting that it does not have the square-symmetry of a relation on a set where A = B. Developments in algebraic logic have facilitated usage of binary relations. The calculus of relations includes the algebra of sets, extended by composition of relations and the use of converse relations. The inclusion R ⊂ S, meaning that aRb implies aSb, sets the scene in a lattice of relations. But since P ⊂ Q ≡ ( P ∩ Q ¯ = ∅ ) ≡ ( P ∩ Q = P ) , {\displaystyle P\subset Q\equiv (P\cap {\bar {Q}}=\varnothing )\equiv (P\cap Q=P),} the inclusion symbol is superfluous. Nevertheless, composition of relations and manipulation of the operators according to Schröder rules, provides a calculus to work in the power set of A × B.