SWISH -- SWI-Prolog for SHaring

/* Facts */
man(dr_black).
man(reverend_green).
man(colonel_mustard).
man(professor_plum).

woman(mrs_peacock).
woman(madame_rose).
woman(miss_scarlett).
woman(mrs_white).

victim(dr_black).

playing_cards(colonel_mustard).
playing_cards(reverend_green).
playing_cards(mrs_peacock).

gardening(mrs_white).
gardening(reverend_green).

played_golf(professor_plum).
played_golf(colonel_mustard).

smoker(miss_scarlett).
smoker(colonel_mustard).
smoker(mrs_white).
smoker(dr_black).
smoker(mrs_peacock).

room(room_21).
room(room_22).
room(room_23).
room(room_24).
room(room_25).

stay_in(dr_black,room_22).
stay_in(reverend_green,room_24).
stay_in(miss_scarlett,room_21).
stay_in(colonel_mustard,room_24).
stay_in(professor_plum,room_22).
stay_in(mrs_peacock,room_23).
stay_in(madame_rose,room_21).
stay_in(mrs_white,room_23).

owns_revolver(reverend_green).
owns_revolver(colonel_mustard).
owns_revolver(madame_rose).

/* Rules */
suspect(X):- man(X), \+victim(X).
suspect(X):- woman(X), \+victim(X).

has_alibi(X):- suspect(X), playing_cards(X).

went_outside(X):- gardening(X).
went_outside(X):- smoker(X).
went_outside(X):- played_golf(X).

share_room(X,Y):- room(R), stay_in(X,R), stay_in(Y,R), X \= Y.

revolver_access(X):- owns_revolver(X).
revolver_access(X):- share_room(X,Y), owns_revolver(Y).

/* Step 1: Query this knowledge base to find the murderer amongst all the suspects. */

/* Step 2: Write a new rule to list all the suspects, who went outside (we found some muddy footprints on the carpet next to Dr Black’s body), who have no alibi and who had access to a revolver!*/
/* guilty(X):- ....... */