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§6, p. 470 — corrected count of requests served by a fixed run

Proved
ObliviousRAM.LowerBound.card_satisfied_le

by mikedeng1 · Oct 6, 2026 · Mathlib 0df444a (Lean v4.33.1)

corrected-boundcountingoblivious-ramp2o-batch-pfp2ap2o-gran-per-chapterp2o-plan-paperp2o-v1

Fix a run aaa of qqq accesses, a hand capacity bbb, and ttt request rounds. The number of request sequences that this run legally satisfies is bounded by

∣{r:a⊨r}∣≤multichoose⁡(q,t) bt.|\{r:a\models r\}|\le \operatorname{multichoose}(q,t)\,b^t.∣{r:a⊨r}∣≤multichoose(q,t)bt.

This bounds the request sequences associated with a single hidden action history, retaining the paper's non-strict round-end indices.

Formalization Note The printed proof says bqb^qbq and footnote 29 offers (qt)bt\binom qt b^t(tq​)bt; both fail when round ends repeat. With m=b=q=2m=b=q=2m=b=q=2 and t=7t=7t=7, a run that takes both balls serves all 272^727 request sequences, exceeding bq=4b^q=4bq=4 while (qt)=0\binom qt=0(tq​)=0. The formal bound uses Nat.multichoose q t, equal to (q+t−1t)\binom{q+t-1}{t}(tq+t−1​) when q≥1q\ge1q≥1, and is the corrected statement needed for Theorem 6.1. No legality hypothesis is needed: an illegal run satisfies no requests.

Preamble
import Mathlib
import Definitions.Def_ObliviousRAM_LowerBound_Game
Formal statement
namespace ObliviousRAM.LowerBound
open Classical

theorem card_satisfied_le {b m t : ℕ} (a : List (Action m)) :
    (Finset.univ.filter fun r : Fin t → Fin m => Satisfies b a r).card ≤
      Nat.multichoose a.length t * b ^ t := by sorry

end ObliviousRAM.LowerBound
Source
Goldreich and Ostrovsky, Software protection and simulation on oblivious RAMs, J. ACM 43 (1996), p. 470, §6, proof of THEOREM 6.1 and footnote 29 (printed bounds corrected); https://doi.org/10.1145/233551.233553
Human review
  • Endorsed by Shuze Chen · Oct 6, 2026

    Confirmed by the moderator at approval.

  • Endorsed by mikedeng1 · Oct 6, 2026

    Confirmed by the mission captain (proposal self-audit).

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