simp only [List.toFinset_nil, Finset.coe_empty, Set.union_empty] at s1
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
stack : List Node
s1 : ↑(dft_aux g stack []).toFinset ⊆ reachable_from_list g stack ∪ ↑[].toFinset
⊢ ↑(dft_aux g stack []).toFinset = reachable_from_list g stack
Node : Type
inst✝ : DecidableEq Node
g : Graph Node
stack : List Node
s1 : ↑(dft_aux g stack []).toFinset ⊆ reachable_from_list g stack
⊢ ↑(dft_aux g stack []).toFinset = reachable_from_list g stack