simp only [header, Schema.sieve_eq_List_sieve]
η : Type u_η
dec_η : DecidableEq η
sch : Schema
hu : Schema.Unique sch
t : Table sch
bs : List Bool
h : List.length bs = ncols t
i : Nat
hlt : i < ncols t
⊢ List.get (header t) { val := i, isLt := (_ : i < List.length (header t)) } ∈ header (selectColumns1 t bs) ↔
    List.get bs { val := i, isLt := (_ : i < List.length bs) } = true
η : Type u_η
dec_η : DecidableEq η
sch : Schema
hu : Schema.Unique sch
t : Table sch
bs : List Bool
h : List.length bs = ncols t
i : Nat
hlt : i < ncols t
⊢ List.get (Schema.names sch) { val := i, isLt := (_ : i < List.length (header t)) } ∈
      Schema.names (List.sieve bs sch) ↔
    List.get bs { val := i, isLt := (_ : i < List.length bs) } = true