Vu Phan

Results 3 issues of Vu Phan

@iensen :grin: Below is a CR-Prolog program: ``` predicates a(). b(). c(). rules a. -a :- not b, not c. b :+. c :+. b :- c. c :- b....

`:- #count{X1 : p(X1)} > 0, q(X1).` should produce an error or a warning