Two terms unify if and only if it follows from the previous three clauses that they unify.(For example, it is not possible to instantiate variable X to mia when unifying one pair of arguments, and to instantiate X to vincent when unifying another pair of arguments. the variable instantiations are compatible.all their corresponding arguments unify, and.They have the same functor and arity (number of arguments a complex term takes), and.

If term1 and term2 are complex terms, then they unify if and only if:.

(So if they are both variables, they’re both instantiated to each other, and we say that they share values.)

Similarly, if term2 is a variable and term1 is any type of term, then term1 and term2 unify, and term2 is instantiated to term1. If term1 is a variable and term2 is any type of term, then term1 and term2 unify, and term1 is instantiated to term2.If term1 and term2 are constants, then term1 and term2 unify if and only if they are the same atom, or the same number.god(zeus) and god(X) unify by assigning X the value zeus.Ī precise definition of unification from the Learn Prolog Now tutorial: Plato and plato unfiy because they are the same atom 42 and 42 unify because they are the same number X and X unify because they are the same variable human(plato) and human(plato) unify because they are the same complex term.Ĭonstants and variables can unify if the variable has the same value as the atom or the number. Complex terms: Have the form functor(term_1.Variables: Always start with an uppercase letter ( X, Head, A42.Constants: Either atoms ( plato) or numbers ( 42).In the example above Prolog unified X with zeus and apollo and Y with socrates, aristotle and plato. Prolog can answer our queries by using unification and proof search (including backtracking).

Block world problem in prolog