Theorem: selectColumns2_spec4 (Table/Proofs.lean)

State before:
η : Type u_η
dec_η : DecidableEq η
sch : Schema
⊢ ∀ (t : Table sch) (ns : List (Fin (ncols t))), nrows (selectColumns2 t ns) = nrows t
Tactic:
intro t ns
State after:
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
ns : List (Fin (ncols t))
⊢ nrows (selectColumns2 t ns) = nrows t

State before:
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
ns : List (Fin (ncols t))
⊢ nrows (selectColumns2 t ns) = nrows t
Tactic:
simp only [nrows, selectColumns2, Schema.length_eq_List_length]
State after:
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
ns : List (Fin (ncols t))
⊢ List.length (List.map (Row.nths ns) t.rows) = List.length t.rows

State before:
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
ns : List (Fin (ncols t))
⊢ List.length (List.map (Row.nths ns) t.rows) = List.length t.rows
Tactic:
apply List.length_map
State after:
no goals