{V : Type u} →
  {G : SimpleGraph V} →
    {motive : (a a_1 : V) → G.Walk a a_1 → Sort u_1} →
      {a a_1 : V} → (t : G.Walk a a_1) → t.ctorIdx = 0 → ({u : V} → motive u u SimpleGraph.Walk.nil) → motive a a_1 t