Quasi-identity
In universal algebra, a quasi-identity is an implication of the form
where s1,..., sn, t1,..., tn, s, and t are terms built up from variables using the operation symbols of the specified signature.
A quasi-identity amount to a conditional equation for which the conditions themselves are equations. Alternatively, it can be seen as a disjunction of equations s1 = t1 ∨... ∨ sn = tn ∨ s = t. A quasi-identity for which n = 0 is an ordinary identity or equation, whence quasi-identities are a generalization of identities. Quasi-identities are special type of Horn clauses.
