Unification followed by unfolding. The left-hand side of a rule is unified with some term, resulting in a set of variable bindings. The term is then replaced by the right-hand side of the rule with values substituted for {bound variable}s.

In addition suitable contents:
[ = ] [ al ] [ am ] [ an ] [ ar ] [ arc ] [ at ] [ b ] [ bi ] [ bo ] [ bound variable ] [ bs ] [ by ] [ ca ] [ cat ] [ ch ] [ de ] [ ding ] [ du ] [ ed ] [ er ] [ es ] [ et ] [ fi ] [ file ] [ fo ] [ for ] [ gh ] [ gs ] [ h ] [ hr ] [ ht ] [ id ] [ ie ] [ il ] [ in ] [ io ] [ is ] [ it ] [ la ] [ ld ] [ Lex ] [ lt ] [ lu ] [ mo ] [ mod ] [ module ] [ na ] [ nf ] [ ng ] [ ni ] [ om ] [ ph ] [ pl ] [ query ] [ rc ] [ re ] [ ru ] [ se ] [ set ] [ si ] [ so ] [ st ] [ su ] [ T ] [ th ] [ unfold ] [ va ] [ value ] [ var ] [ variable ]