!7

class Prop implements IStatement {}

record $HappensBefore$<A, B>(A event1, B event2) extends Prop {}
record $HappensAtDay$<A, B>(A event, B y) extends Prop {}
record $LessThan$<A, B>(A x, A y) extends Prop {}

// we can fully define a statement on primitive values
full define $LessThan(int x, int y) = x < y;

// we can output a variable
full define $LessThan(int x, var y) = y := any int bigger than x;

/*
  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.
*/