% File: crypto.pro of directory xsolve1
% Type: Prolog source
% Line: cryptores.pro
% Date: Fall 2009

%----------------------------------------------------------------------
% load some files

:- consult('combosets.pro').

crypto(N1,N2,Goal,ex(N1,+,N2)) :- Goal is (N1 + N2).
crypto(N1,N2,Goal,ex(N1,*,N2)) :- Goal is (N1 * N2).
crypto(N1,N2,Goal,ex(N1,-,N2)) :- Goal is (N1 - N2).
crypto(N1,N2,Goal,ex(N1,-,N2)) :- Goal is (N2 - N1).
crypto(N1,N2,Goal,ex(N1,/,N2)) :- N2 > 0, Goal is (N1 / N2).
crypto(N1,N2,Goal,ex(N1,/,N2)) :- N1 > 0, Goal is (N2 / N1).

crypto(N1,N2,N3,G,Expr) :-
  combos(set(N1,N2,N3), combo(A,B), extra(C)),
  crypto(A,B,SG,SGE),
  crypto(C,SG,G,UGE),
  substitute(SGE,SG,UGE,Expr).

crypto(N1,N2,N3,N4,G,Expr) :-
  combos(set(N1,N2,N3,N4), combo(A,B), extras(C,D)),
  crypto(A,B,SG,SGE),
  crypto(C,D,SG,G,UGE),
  substitute(SGE,SG,UGE,Expr).

%----------------------------------------------------------------------
% key substitution code

substitute(New,Old,ex(Old,O,Z), ex(New,O,Z)).
substitute(New,Old,ex(X,O,Old), ex(X,O,New)).
substitute(New,Old,ex(X,O,Z), ex(Q,O,Z)) :-
  substitute(New,Old,X,Q).
substitute(New,Old,ex(X,O,Z), ex(X,O,Q)) :- 
  substitute(New,Old,Z,Q).