/**
         
 * Modern Albufeira Prolog Interpreter
         
 *
         
 * Warranty & Liability
         
 * To the extent permitted by applicable law and unless explicitly
         
 * otherwise agreed upon, XLOG Technologies AG makes no warranties
         
 * regarding the provided information. XLOG Technologies AG assumes
         
 * no liability that any problems might be solved with the information
         
 * provided by XLOG Technologies AG.
         
 *
         
 * Rights & License
         
 * All industrial property rights regarding the information - copyright
         
 * and patent rights in particular - are the sole property of XLOG
         
 * Technologies AG. If the company was not the originator of some
         
 * excerpts, XLOG Technologies AG has at least obtained the right to
         
 * reproduce, change and translate the information.
         
 *
         
 * Reproduction is restricted to the whole unaltered document. Reproduction
         
 * of the information is only allowed for non-commercial uses. Selling,
         
 * giving away or letting of the execution of the library is prohibited.
         
 * The library can be distributed as part of your applications and libraries
         
 * for execution provided this comment remains unchanged.
         
 *
         
 * Restrictions
         
 * Only to be distributed with programs that add significant and primary
         
 * functionality to the library. Not to be distributed with additional
         
 * software intended to replace any components of the library.
         
 *
         
 * Trademarks
         
 * Jekejeke is a registered trademark of XLOG Technologies AG.
         
 */
         

         
subtract([], _, []).
         
:-(subtract('.'(X, L), R, T), ','(member(X, R), ','(!, subtract(L, R, T)))).
         
:-(subtract('.'(X, L), R, '.'(X, S)), subtract(L, R, S)).
         
intersection([], _, []).
         
:-(intersection('.'(X, L), R, T), ','(member(X, R), ','(!, ','(=(T, '.'(X, S)), intersection(L, R, S))))).
         
:-(intersection('.'(_, L), R, S), intersection(L, R, S)).
         
union([], T, T).
         
:-(union('.'(X, L), R, S), ','(member(X, R), ','(!, union(L, R, S)))).
         
:-(union('.'(X, L), R, '.'(X, S)), union(L, R, S)).
         
:-(symdiff(L, R, S), ','(subtract(L, R, H), ','(subtract(R, L, J), append(H, J, S)))).
         
subset([], _).
         
:-(subset('.'(X, Y), Z), ','(member(X, Z), ','(!, subset(Y, Z)))).
         
disjoint([], _).
         
:-(disjoint('.'(X, _), Z), ','(member(X, Z), ','(!, fail))).
         
:-(disjoint('.'(_, Y), Z), disjoint(Y, Z)).
         
:-(equal(L, R), ','(subset(L, R), subset(R, L))).