have s1 : ys = []
α : Type
inst✝ : DecidableEq α
ys : List α
h1 : [].length = ys.length
h2 : [].Nodup
h3 : ys.Nodup
⊢ ∃ f, InjOn f [] ∧ map f [] = ys
case s1
α : Type
inst✝ : DecidableEq α
ys : List α
h1 : [].length = ys.length
h2 : [].Nodup
h3 : ys.Nodup
⊢ ys = []

α : Type
inst✝ : DecidableEq α
ys : List α
h1 : [].length = ys.length
h2 : [].Nodup
h3 : ys.Nodup
s1 : ys = []
⊢ ∃ f, InjOn f [] ∧ map f [] = ys