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Uniform runtime transfer between the two WordRAM models

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WordRAM.APSPBridge.uniform_time_transfer

by wurtle · Nov 2, 2026 · Mathlib 0df444a (Lean v4.33.1)

fine-grained-complexityruntime-transferwordram

There is a natural overhead exponent ddd such that for every problem QQQ whose input and observable output are bounded by B(n)=K(n+1)qB(n)=K(n+1)^qB(n)=K(n+1)q, every input-magnitude exponent κ\kappaκ, and every correct source program with runtime T(n)T(n)T(n) at all sufficiently large word widths, there is a fixed target program, width threshold coefficient, and positive CCC solving the same problem in C(T(n)+B(n)+1)(⌊log⁡2n⌋+1)dC(T(n)+B(n)+1)(\lfloor \log_2 n \rfloor+1)^dC(T(n)+B(n)+1)(⌊log2​n⌋+1)d steps. This holds in both directions between the signed-pointer and unsigned-pointer models, including input packing and output recovery, and the same bound works at every sufficiently large physical width. This is the quantitative half of the equivalence; it does not assert the operational simulation clauses.

Preamble
import Definitions.Def_WordRAM_APSP_Bridge

set_option autoImplicit false
Formal statement
theorem WordRAM.APSPBridge.uniform_time_transfer : ∃ d : Nat, WordRAM.APSPBridge.UniformTimeTransfer d := by sorry
Source
Torben Hagerup, Sorting and Searching on the Word RAM, STACS 1998, pp. 366-398, model conventions pp. 369-372, https://doi.org/10.1007/BFb0028575; Josh Alman and Virginia Vassilevska Williams, Truly Subquadratic 3SUM and Truly Subcubic APSP via Triangles in Sparse Lopsided Graphs, 2026, https://arxiv.org/abs/2610.06783; mission 'Two WordRAM models: equivalence with polylogarithmic overhead'.

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