prolog::arg0/3

arg0( +Index, +Term , -Arg )*

Similar to arg//33, but arg0(0,_T_,_F_) unifies F with T's principal functor:


 ?- arg0(0, f(a,b), A).
 A = f.
 ?- arg0(1, f(a,b), A).
 A = a.
 ?- arg0(2, f(a,b), A).
 A = b.

Private-func:

1. prolog::arg0_3::arg0/3(int ARG1, int ARG2, int ARG3)():