pub trait DecidableRel<A> { // Required method fn decide_rel(&self, a: &A, b: &A) -> Decision<()>; // Provided method fn holds(&self, a: &A, b: &A) -> bool { ... } }
A decidable binary relation R : A → A → Prop.
R : A → A → Prop
Decide whether R(a, b) holds.
R(a, b)
Check whether R(a, b) holds.