One or Two Things About Prolog

Prolog is different from most programming languages in that it does not presuppose a von Neumann architecture and does not have assignment as the basic underlying operation (Warren 1981c). The primitive unit is not an instruction, but a theorem of first order logic, called a clause. Variables inside clauses are universally quantified and may be substituted by well-formed formulas, but predicates cannot be quantified. Unlike conventional languages such as FORTRAN and PASCAL, Prolog is well suited to parallel processing machines because program evaluations can be run in any order without regard to sequence.