Class RandomOracle: Type := {
  ro_question: Type;
  ro_answer: ro_question -> Type;
  ro_default_question: ro_question;
  ro_default_answer: ro_answer ro_default_question
}.Class RandomOracle: Type := {
  ro_question: Type;
  ro_answer: ro_question -> Type;
  ro_default_question: ro_question;
  ro_default_answer: ro_answer ro_default_question
}.Class RandomOracle: Type := {
  ro_question: Type;
  ro_answer: ro_question -> Type;
  ro_default_question: ro_question;
  ro_default_answer: ro_answer ro_default_question
}.Class RandomOracle: Type := {
  ro_question: Type;
  ro_answer: ro_question -> Type;
  ro_default_question: ro_question;
  ro_default_answer: ro_answer ro_default_question
}.Class RandomOracle: Type := {
  ro_question: Type;
  ro_answer: ro_question -> Type;
  ro_default_question: ro_question;
  ro_default_answer: ro_answer ro_default_question
}.Definition RandomQA {ora: RandomOracle}: Type := {q: ro_question & ro_answer q}.Definition RandomHistory {ora: RandomOracle}: Type := {h: nat -> option RandomQA | forall x y, x < y -> h x = None -> h y = None}.Definition history_get {ora: RandomOracle} (h: RandomHistory) (n: nat) := proj1_sig h n.

Lemma history_sound2: forall {ora: RandomOracle} (h: RandomHistory) (x y: nat), x <= y -> (exists a, h y = Some a) -> (exists a, h x = Some a).