// RESULT: 0.6
	Pmax=? [ !"b" U "a" ];
	// RESULT: ?
	"ex1f": P<=0.5 [ !"b" U "a" ];
	// RESULT: true
	filter(forall, "ex1f" <=> (x=3));

	// RESULT: 0.6
	Pmin=? [ !"b" U "a" ];
	// RESULT: ?
	"ex2f": P>=0.5 [ !"b" U "a" ];
	// RESULT: true
	filter(forall, "ex2f" <=> (x=0|x=1|x=2));