;                  PROLOG 'BOOT' PROGRAM
; contains definitions for some 'system' predicates which are defined
; in Prolog rather than hard-coded in the interpreter.
; you may add your own definitions and queries like
; ? paper(0), ink(5), window(400,100,60,50).

?paper (0), ink(7),window (512,256,0,0).

?op(21, "not").
not X <- X,!,fail.
not X.

cls <- cls(0).
clause([Head|Body])  <- clause (Head, Body).
retract ([Head|Body])  <- retract (Head,Body).

append ([],Ys,Ys).
append ([X|Xs],Ys,[X|Zs])   <-  append (Xs, Ys, Zs).

member (X,[X|Xs]). 
member (X,[Y|Ys]) <- member(X,Ys).

writeln ([X|Y]) <- !, write(X),writeln(Y).
writeln([]) <- nl.