simp only [nrows, dropColumns, Schema.length_eq_List_length]
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
cs : ActionList Schema.removeCertifiedName sch
⊢ nrows (dropColumns t cs) = nrows t
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
cs : ActionList Schema.removeCertifiedName sch
⊢ List.length (List.map (Row.removeColumns cs) t.rows) = List.length t.rows