intro a hyp'
case right
α : Type
inst✝ : LinearOrder α
l : List α
head : α
tail : List α
hyp : head :: tail ≠ []
⊢ ∀ a ∈ tail, (if c : tail = [] then head else min head (smallest tail c)) ≤ a
case right
α : Type
inst✝ : LinearOrder α
l : List α
head : α
tail : List α
hyp : head :: tail ≠ []
a : α
hyp' : a ∈ tail
⊢ (if c : tail = [] then head else min head (smallest tail c)) ≤ a