Forall/2, foreach/2, double negation, relational division and SQL

[chansey97]

@j4n_bur53

foreach(p(X), q(Y,X)) <=> r(Y), forall(p(X), q(Y,X)) 

forall/2 and foreach/2 are interchangeable only if Y is a ground value when executing forall/2 and foreach/2, see On a logical reading of `foreach/2` predicate - #15 by chansey97

For your example,

?- retractall(course(_)),
   foreach(course(CName), student_course(SName, CName)).
true.

?- retractall(course(_)),
   student(SName), forall(course(CName), student_course(SName, CName)).
SName = alice ;
SName = bob ;
SName = clark ;
SName = david ;
SName = emily ;
SName = gavin ;
SName = ferry.