/**
 * @file A join-semilattice (or upper semilattice) is a semilattice whose operation is called `join`, and which can be thought
 * of as a least upper bound.
 *
 * A `JoinSemilattice` must satisfy the following laws:
 *
 * - Associativity: `a ∨ (b ∨ c) = (a ∨ b) ∨ c`
 * - Commutativity: `a ∨ b = b ∨ a`
 * - Idempotency:   `a ∨ a = a`
 *
 */