simp only [head, nrows, List.dropLastN, Function.comp, h,
           Schema.length_eq_List_length, ite_true]
case mk
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
z : Int
prop✝ : Int.abs z < nrows t
h : z < 0
prop : Int.abs z < List.length t.rows
⊢ nrows (head t { val := z, property := prop✝ }.val) = nrows t - Int.abs { val := z, property := prop✝ }.val
case mk
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
z : Int
prop✝ : Int.abs z < nrows t
h : z < 0
prop : Int.abs z < List.length t.rows
⊢ List.length (List.reverse (List.drop (Int.abs z) (List.reverse t.rows))) = List.length t.rows - Int.abs z