!7

/*
    Event 1 happens before event 2 :=
      vars {event 1, event 2, X, Y}
      Event 1 happens at day X.
      Event 2 happens at day Y.
      X < Y.

*/

sclass Obj {
  class Fact {}
  
  record $HappensBefore$<A, B>(A event1, B event2) extends Fact {}
  record $HappensAtDay$<A, B>(A event, B y) extends Fact {}
  record $LessThan$<A, B>(A x, A y) extends Fact {}
  
  // Enrolling happens before graduation.
  // Enrolling happens at day 200.
  // Graduation happens at day 100. // Contradiction!
  
  L<Fact> facts = ll(
    new $HappensBefore$("enrolling", "graduation"),
    new $HappensAtDay$("enrolling", 200),
    new $HappensAtDay$("graduation", 200)
  );

  *() {
    pnlWithHeading("Facts", facts);
  }
}

p-exp { new Obj; }