n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ range' n (m - n) ++ range' m (l - m) = range' n (l - n)
n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ Ico n m ++ Ico m l = Ico n l
dsimp only [Ico]
case h.e'_2.h.e'_6
n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ range' m (l - m) = range' (n + 1 * (m - n)) (l - m)

case h.e'_3.h.e'_2
n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ l - n = l - m + (m - n)
n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ range' n (m - n) ++ range' m (l - m) = range' n (l - n)
convert range'_append n (m-n) (l-m) 1 using 2
no goals
case h.e'_2.h.e'_6
n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ range' m (l - m) = range' (n + 1 * (m - n)) (l - m)
rw [one_mul, add_tsub_cancel_of_le hnm]
no goals
case h.e'_3.h.e'_2
n m l : ℕ
hnm : n ≤ m
hml : m ≤ l
⊢ l - n = l - m + (m - n)
rw [tsub_add_tsub_cancel hml hnm]