apply min_eq_right
α : Type
inst✝ : LinearOrder α
l : List α
head : α
tail : List α
hyp : head :: tail ≠ []
h : ¬tail = []
h' : ¬head ≤ smallest tail h
⊢ min head (smallest tail h) = smallest tail h
case h
α : Type
inst✝ : LinearOrder α
l : List α
head : α
tail : List α
hyp : head :: tail ≠ []
h : ¬tail = []
h' : ¬head ≤ smallest tail h
⊢ smallest tail h ≤ head