Usage:
Term =.. List

Succeeds if List is a list of the functor and all arguments of Term, in order.

Actually, =.. is defined on Prolog and here is its definition:

 X(|Y)=..[X|Y].

Example:

 ?- f(a, b)=..X, Y=..[g, c, d], write(X), nl, write(Y), nl.