Prolog Language Extra-logical Predicates Meta-logical predicates
Example
Predicates that reason about instantiations are called meta-logical. Examples are:
var/1ground/1integer/1
These predicates are outside the realm of pure monotonic logic programs, because they break properties like commutativity of conjunction.
Other predicates that are meta-logical include:
arg/3functor/3(=..)/2
These predicates could in principle be modeled within first-order logic, but require an infinite number of clauses.
