% INTRO TO LOGIC PROGRAMMING AND AI
% Spring 1998
% //Selmer Bringsjord
%
% The "mini jobs puzzle" runs as follows:

%=============
% Roberta and Steve hold, between them, two jobs.  Each has one job.
% The jobs are teacher and nurse.  The job of nurse is held by a male.
% Who holds which jobs?
%=============
%
% 

set(auto).
assign(max_proofs,-1).

formula_list(usable).

% Everybody is employed:
all x (Job(x,nurse) | Job(x,teacher)).

% Nurses are males:
all x (Job(x,nurse) -> Male(x)).

% Everybody is male or female; no one is both: 
all x ( (Female(x) | Male(x)) & -(Female(x) & Male(x))).

%Roberta is a female and Steve is a male:
Female(roberta).
Male(steve).

% Steve and Roberta are distinct:
steve != roberta.

% If x is a teacher and y is diverse from x, then y is a nurse, and
% y isn't a teacher:
all x all y ( (Job(x,teacher) & x != y) -> Job(y,nurse)).
all x all y ( (Job(x,teacher) & x != y) -> -Job(y,teacher)).

% If x is a nurse and y is diverse from x, then y is a teacher, and
% y isn't a nurse:
all x all y ( (Job(x,nurse) & y != x) -> Job(y,teacher)).
all x all y ( (Job(x,nurse) & y != x) -> -Job(y,nurse)).

% -(Job(roberta,teacher)).
-(Job(steve,nurse)).
%-(Job(steve,nurse)).

% -Job(x,y) | Info(x,y).

end_of_list.

% Templates to have ready for conversion to "database" version of
% the problem.
%
% list(sos).
%
%
% end_of_list.

% list(passive).
% -Info(x,y) | $ANSWER(hasjob(x,y)).
% end_of_list.