. contradiction
case tl
η : Type u_η
dec_η : DecidableEq η
schema : Schema
η✝ : Type u_1
nm : η✝
τ : Type u_2
hs : List Header
a✝ : HasName nm hs
eqt :
  (match nm, hs, HasName.tl a✝ with
    | .(nm), x, HasName.hd => Sum.inl (EqT.refl nm)
    | x, x_1, HasName.tl htl => Sum.inr htl) ≡
    Sum.inl (EqT.refl nm)
⊢ HasName.tl a✝ = HasName.hd
no goals