To see all the facts involving the le relation from the prelude:
Coq < Search le.
le_n: forall n : nat, n <= n
le_S: forall n m : nat, n <= m -> n <= S m
...
max_l: forall n m : nat, m <= n -> Nat.max n m = n
max_r: forall n m : nat, n <= m -> Nat.max n m = m
...
...