/* time point constraints */
% thom fruehwirth ECRC 1991-92, 931223

handler time-point.

option(already_in_store, on). 
option(already_in_heads, on).	% essential for termination of intersect rule
option(check_guard_bindings, off).

operator(700,xfy,'=<+').
operator(700,xfy,'=<*').

	ground(X):- not nonground(X).


constraints (=<+)/2, (=<*)/2.

start(X):- 0=<*X=<*0.

ground @
X=<+Y=<+Z <=> ground(X-Y-Z) | X=<Y, Y=<Z.
ground @
X=<*Y=<*Z <=> ground(X-Y-Z) | X=<Y, Y=<Z.

inconsistent @
A=<*X=<*B <=> A>B | fail.
intersect @
A=<*Y=<*B,C=<*Y=<*D <=> AC is max(A,C), BD is min(B,D) | AC=<*Y=<*BD.

propagate_forward @
A=<*Y=<*B,C=<+Y-Z=<+D ==> AC is A+C , BD is B+D , AC=<*Z=<*BD.
propagate_backward @
A=<*Y=<*B,C=<+Z-Y=<+D ==> AC is A-D , BD is B-C , AC=<*Z=<*BD.


/*
% example in old user-interface:
CRS>   start(X),3=<+X-Y=<+10,4=<+Y-Z=<+5.
3 =<+X - Y =<+10
4 =<+Y - Z =<+5
0 =<* X =<* 0
3 =<* Y =<* 10
7 =<* Z =<* 15

CRS>    start(_0),
	10 =<+_0 - _1 =<+20,
	10 =<+_3 - _2 =<+20,
	30 =<+_1 - _2 =<+40,
	40 =<+_3 - _4 =<+50,
	60 =<+_0 - _4 =<+70.
YES IF
10 =<+_0 - _1 =<+20
10 =<+_3 - _2 =<+20
30 =<+_1 - _2 =<+40
40 =<+_3 - _4 =<+50
60 =<+_0 - _4 =<+70
0 =<* _0 =<* 0
10 =<* _1 =<* 20
20 =<* _3 =<* 30
40 =<* _2 =<* 50
60 =<* _4 =<* 70
*/

% end of handler time-point