no goals
ss : List String
x✝ : List Char
⊢ List.foldl (fun x x_1 => x ++ x_1) { data := x✝ } [] = { data := x✝ ++ List.join (List.map data []) }
simp
no goals
ss✝ : List String
s : List Char
ss : List String
x✝ : List Char
⊢ { data := x✝ ++ s ++ List.join (List.map data ss) } =
    { data := x✝ ++ List.join (List.map data ({ data := s } :: ss)) }
simp