simp [c'']
case right
l : List ℕ
head : ℕ
tail : List ℕ
hyp : head :: tail ≠ []
a : ℕ
hyp' : a ∈ tail
c'' : tail ≠ []
⊢ (if c : tail = [] then head else Nat.min head (smallest tail c)) ≤ a
case right
l : List ℕ
head : ℕ
tail : List ℕ
hyp : head :: tail ≠ []
a : ℕ
hyp' : a ∈ tail
c'' : tail ≠ []
⊢ head ≤ a ∨ smallest tail ⋯ ≤ a