apply List.length_map
η : Type u_η
dec_η : DecidableEq η
sch : Schema
τ : Type u
t✝ : Table sch
c✝ : η
v✝ : τ
hc✝ : Schema.HasCol (c✝, τ) sch
⊢ List.length
      (updateWithoutRetyping [{ fst := (c✝, τ), snd := hc✝ }] t✝ fun r =>
          match Row.getCell r hc✝ with
          | Cell.emp => Row.singleValue v✝
          | Cell.val vOld => Row.singleValue vOld).rows =
    List.length t✝.rows
no goals