Circuits and expressions with non-associative gates

We consider circuits and expressions whose gates carry out multiplication in a non-associative groupoid such as loop. We define a class we call the polyabelian groupoids, formed by iterated quasidirect products of Abelian groups. We show that a loop can express arbitrary Boolean functions if and only if it is not polyabelian, in which case its EXPRESSION EVALUATION and CIRCUIT VALUE problems are NC/sup 1/-complete and P-complete respectively. This is not true for groupoids in general, and we give a counter-example. We show that EXPRESSION EVALUATION is also NC/sup 1/-complete if the groupoid has a non-solvable multiplication semigroup, but is in TC/sup 0/ if the groupoid is both polyabelian and has a solvable multiplication semigroup. Thus, in the non-associative case, earlier results about the role of solvability in circuit complexity generalize in several different ways.

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