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In universal algebra, a quasiidentity is an implication of the form

s1 = t1 ∧ … ∧ sn = tns = t

where s1, ..., sn, s and t1, ..., tn,t are terms built up from variables using the operation symbols of the specified signature.

Quasiidentities amount to conditional equations for which the conditions themselves are equations. A quasiidentity for which n = 0 is an ordinary identity or equation, whence quasiidentities are a generalization of identities. Quasiidentities are special type of Horn clauses.

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