// RESULT: 0.6
	Pmax=? [ !"b" U "a" ];
	// RESULT: ?
	"ex1": P<=0.5 [ !"b" U "a" ];
	// RESULT: true
	filter(forall, "ex1" <=> (x=3));

	// RESULT: 0
	Pmin=? [ !"b" U "a" ];
	// RESULT: ?
	"ex2": P>=0.5 [ !"b" U "a" ];
	// RESULT: true
	filter(forall, "ex2" <=> (x=2));