induction a1
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
xs ys : List Node
h1 : xs ⊆ ys
x : Node
a1 : x ∈ reachable_from_list g xs
⊢ x ∈ reachable_from_list g ys
case base
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
xs ys : List Node
h1 : xs ⊆ ys
x x✝ : Node
a✝ : x✝ ∈ xs
⊢ x✝ ∈ reachable_from_list g ys

case step
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
xs ys : List Node
h1 : xs ⊆ ys
x x✝ : Node
e✝ : Node × List Node
a✝² : e✝ ∈ g
a✝¹ : x✝ ∈ e✝.2
a✝ : reachable_from_list g xs e✝.1
a_ih✝ : e✝.1 ∈ reachable_from_list g ys
⊢ x✝ ∈ reachable_from_list g ys