arg/3¶

"arg(+ N,+ T, A" ) is iso

Succeeds if the argument N of the term T unifies with A. The arguments are numbered from 1 to the arity of the term.

The current version will generate an error if T or N are unbound, if T is not a compound term, of if N is not a positive integer. Note that previous versions of YAP would fail silently under these errors.