induction a1
α : Type
inst : DecidableEq α
g : Graph α
xs : List α
h1 : ∀ (a x : α), x ∈ xs → ∀ (x_1 : List α), a ∈ x_1 → (x, x_1) ∈ g → a ∈ xs
a : α
a1 : a ∈ reachable_from_list g xs
⊢ a ∈ xs
case base
α : Type
inst : DecidableEq α
g : Graph α
xs : List α
h1 : ∀ (a x : α), x ∈ xs → ∀ (x_1 : List α), a ∈ x_1 → (x, x_1) ∈ g → a ∈ xs
a x✝ : α
a✝ : x✝ ∈ xs
⊢ x✝ ∈ xs

case step
α : Type
inst : DecidableEq α
g : Graph α
xs : List α
h1 : ∀ (a x : α), x ∈ xs → ∀ (x_1 : List α), a ∈ x_1 → (x, x_1) ∈ g → a ∈ xs
a x✝ : α
e✝ : α × List α
a✝² : e✝ ∈ g
a✝¹ : x✝ ∈ e✝.2
a✝ : reachable_from_list g xs e✝.1
a_ih✝ : e✝.1 ∈ xs
⊢ x✝ ∈ xs