/*
no
   ?- s([throws(mary),throws(john),break],P).
P = 0.46 ?
yes
   ?- s([throws(mary),throws(john),\+break],P).
P = 0.04 ?
yes
   ?- s([\+ throws(mary),throws(john),break],P).
P = 0.3 ?
yes
   ?- s([\+ throws(mary),throws(john),\+ break],P).
P = 0.2 ?
yes
   ?-
	 */

break : 0.8 :- throws(mary).
break : 0.6 :- throws(john).
throws(mary) : 0.5.
throws(john).
