Lean4
/-- `a : α` is a top element of `α` if it is greater than or equal to any other element of `α`.
This predicate is roughly an unbundled version of `OrderBot`, except that a preorder may have
several top elements. When `α` is linear, this is useful to make a case disjunction on
`NoMaxOrder α` within a proof. -/
def IsTop (a : α) : Prop :=
∀ b, b ≤ a