Definition fin_history {ora: RandomOracle} (h: list RandomQA) : RandomHistory.Definition inf_history {ora: RandomOracle} (h: nat -> RandomQA) : RandomHistory.Definition fstn_history {ora: RandomOracle} (n: nat) (h: RandomHistory) : RandomHistory.Definition history_coincide {ora: RandomOracle} (n: nat) (h1 h2: RandomHistory): Prop :=
  forall m, m < n -> h1 m = h2 m.(*
Definition history_cons {ora: RandomOracle} (h1: RandomHistory) (a: RandomQA) (h2: RandomHistory): Prop :=
  exists n,
    history_coincide n h1 h2 /\
    h1 n = None /\
    h2 n = Some a /\
    h2 (S n) = None.
*)

Definition history_app {ora: RandomOracle} (h1 h2 h: RandomHistory): Prop :=
  exists n,
    h1 n = None /\
    history_coincide n h1 h /\
    (forall m, h (m + n) = h2 m).Definition is_fin_history {ora: RandomOracle} (h: RandomHistory): Prop :=
  exists n, h n = None.Definition is_inf_history {ora: RandomOracle} (h: RandomHistory): Prop :=
  forall n, h n <> None.Definition is_n_history {ora: RandomOracle} (n: nat) (h: RandomHistory): Prop :=
  h n = None /\ forall n', n' < n -> h n' <> None.Definition is_at_least_n_history {ora: RandomOracle} (n: nat) (h: RandomHistory): Prop :=
  forall n', n' < n -> h n' <> None.

Lemma inf_history_inf {ora: RandomOracle}: forall f, is_inf_history (inf_history f).