Definition emb_trans (I J K : interp domain eta) :
    embedding I J -> embedding J K -> embedding I K.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Class kmodel :=
    {
      nodes : Type ;

      reachable : nodes -> nodes -> Prop ;
      reach_refl u : reachable u u ;
      reach_tran u v w : reachable u v -> reachable v w -> reachable u w ;

      world : nodes -> interp domain eta ;

      world_f : forall u v, reachable u v -> embedding (world u) (world v)
    }.Implicit Type b : logic.Notation "! M" := (kcast _ M) (at level 10).

Lemma eval_invar u v : reachable u v -> forall rho t, @eval _ _ (world u) rho t = @eval _ _ (world v)rho t.