 A model of a theory is a structure for which all the equations of that theory are identities. Terms are built up from variables and constants using the operations of the theory. An equation is a pair of terms; it is satisfied by an algebra when the two terms are equal under all valuations of (assignments of values to) the \(n\) variables appearing in the terms, equivalently when they denote the same \(n\)-ary operation. A quasiequation is a pair consisting of a finite set of equations, called the premises or antecedents, and another equation, the conclusion; it is satisfied by an algebra when the two terms of the conclusion are equal under all valuations of the \(n\) variables appearing in the terms satisfying the premises. A first order formula is a quantified Boolean combination of relational terms.