Plectis
Erdős problem #257

Reciprocal sums over infinite exponent supports

Is the sum of 1/(2^n-1) over every infinite set of positive exponents irrational?

Open 1 Lean modules 4 main results Source directory

What is checked in Lean

  • That the strict Mersenne tail inequality is hereditary under deleting an arbitrary collection of future weights.
  • That binary digit strings restricted to any chosen support retain unique Mersenne coding.
  • Restricted sets are compact and nowhere dense; infinite-support sets are perfect; finite-complement measure is 2^(-|F|), otherwise zero.

Main results

Statements and boundaries are copied from the corpus record. Registry status: not_registered; the claim registry does not carry these declarations and kernel checking them does not promote them into reviewed public claims

mixed prior-art geometry and locally proved metric result; novelty unassessed family: achievement_set_geometry

The base-2 Mersenne achievement set has Lebesgue measure exactly one.

This does not decide whether every infinite-support sum is irrational.

formalisation of an existing theorem family: known_irrational_supports

For every integer base b >= 2, the full-support Erdos-Borwein series is irrational.

This is the classical full-support theorem, not universal Erdos #257.

locally proved result; novelty unassessed family: finite_period_noncollapse

For a reduced finite Mersenne sum, the base order modulo the denominator equals the support lcm.

The finite-support theorem does not settle any infinite-support sum.

What is not checked

  • The universal irrationality problem, or irrationality for any new infinite support.
  • Fair-bit laws, finer singularity results, and periodic-stride dimensions.
  • Any bridge from geometric uniqueness or measure rigidity to arithmetic irrationality.

Open obligations

Prove any one of these and the corresponding reduction above becomes unconditional.

  • arithmetic_rigidity_for_thin_supports Convert hereditary unique coding into an arithmetic obstruction to rational values for every infinite support, including zero-measure Cantor supports.
  • formalise_measure_and_stride_geometry Extend the measure dichotomy to Bernoulli laws and periodic-stride dimensions without implying arithmetic consequences.

Lean modules

ModuleLinesDeclarationsTheorems
ErdosProblems.Erdos257.MersenneSubseriesRigidity 421 28 23

Comparator review

The Comparator replays selected exact interfaces against a pinned toolchain. It never widens what Lean proved.

Replayed by the Comparator

Statement and type parity replayed against the pinned toolchain.

  • The multiplicative order of the base modulo a reduced finite-sum denominator is the support lcm, forcing denominator growth.

    A finite-support denominator theorem does not settle an infinite-support sum.

    finite_period_noncollapse · targeted

  • Full, factorial, power-of-two, multiple, pairwise-coprime, eventually periodic, residue-class, and odd supports are formalised.

    Structured known families do not cover arbitrary infinite supports.

    known_irrational_supports · targeted_full_support_representative

  • Compactness, perfectness, total disconnectedness, nowhere density, and measure one for the unrestricted achievement set.

    Geometry of the full set does not decide irrationality of every coded point.

    achievement_set_geometry · targeted_measure_theorem

  • Support-restricted coding is injective and the associated achievement set has exact finite-complement measure or zero for infinite complement.

    The measure dichotomy does not classify rational points.

    restricted_achievement_sets · targeted_measure_dichotomy

Outside the Comparator selection

Stated in the corpus; not part of the replayed interface set.

  • Rational infinite supports force unbounded scaled tails, sublogarithmic zero windows, and reciprocal-mass constraints.

    The constraints do not exclude every infinite support.

    rational_support_constraints · not_selected_deep_support_vocabulary

  • Lean checks squarefree incidence and no-go statements; the irrationality conclusion uses an external analytic theorem in the paper.

    Comparator must not badge the paper-plus-external conclusion.

    squarefree_support · not_applicable_to_external_irrationality_input

  • Exact greedy characterisations and finite-support exclusions isolate the remaining 1/2 and 1/21 alternatives.

    Neither membership question is decided.

    half_and_twenty_one_frontiers · not_selected_deep_greedy_state_vocabulary

The paper

Problem note 21 pp

Denominator Periods, Rational-Value Constraints and Achievement-Set Geometry

For every finite support and integer base, the reduced denominator has multiplicative order exactly the support lcm. Restricted achievement sets also receive exact coding, topology, perfectness, and measure statements with their finite/infinite hypotheses. Rational infinite supports must satisfy explicit long-division and divisor-incidence constraints, but those constraints do not conflict. Prime support at base 2 and squarefree support at power-of-two bases are cited prior results, not contributions here. The targets 1/2 and 1/21 reduce to open infinite-orbit alternatives; Erdős #257 remains open.