Lean4
theorem leRec_trans {n m k} {motive : (m : ℕ) → n ≤ m → Sort*} (refl le_succ_of_le) (hnm : n ≤ m) (hmk : m ≤ k) :
leRec (motive := motive) refl le_succ_of_le (Nat.le_trans hnm hmk) =
leRec (leRec refl (fun _ h => le_succ_of_le h) hnm) (fun _ h => le_succ_of_le <| Nat.le_trans hnm h) hmk :=
by
induction hmk with
| refl => rw [leRec_self]
| step hmk ih => rw [leRec_succ _ _ (Nat.le_trans hnm hmk), ih, leRec_succ]