Plectis
Erdős problem #1049

Lambert-type series at rational bases

For which rational bases is the corresponding series irrational? The smallest resistant explicit base is three halves.

Open 6 Lean modules 2 main results Source directory

What is checked in Lean

  • That a literal coordinatewise transfer of the integer-base clearing argument forces a power-versus-linear inequality, and that this inequality is impossible at base three halves.
  • The exact denominator-cleared rational-base tail recurrence, including its forcing term.
  • That for every noninteger base with denominator at least two the forcing magnitude grows at least exponentially, while at denominator one it collapses to a bounded expression.
  • The complete elementary Archimedean height inequality used by the published Bundschuh-Väänänen criterion at base seven halves; the analytic irrationality theorem itself remains external.
  • Polynomial bounds on the doubled denominator exponents in the homogenised Padé construction, together with an exact gap identity.
  • The exact exterior-determinant elimination identity, and that rowwise contents scale the Padé errors, exterior determinant, and absolute determinant height by the same factors.
  • The exact Heine-Zudilin cone endpoint exponent arithmetic used to identify the bottom and top coefficient endpoints.
  • That homogeneous evaluation at (3,2) sees only the constant endpoint modulo three and the top endpoint modulo two, so unit endpoints obstruct common local factors.
  • That under unit top and constant endpoint hypotheses, a common multiplier of the two specialised coefficient channels is divisible by neither two nor three; the missing local gain must therefore survive primitive normalisation.
  • That vanishing of the higher bottom and top endpoint jets is exactly divisibility by the corresponding powers of three and two.
  • That the source integer-base ratio inequality implies a strictly negative scalar product-formula margin at three halves.
  • That the four-jet target has exact cardinality (3^R)^2(2^S)^2 and, for positive R, any family with n at least 4R+2S forces two distinct binary selectors to collide; their {-1,0,1} difference cancels all four endpoint jets.
  • That the rectangular Hermite-Pade threshold never improves on the classical one in the checked exponent model, with equality characterised exactly.
  • The exact 81/200 height region: 31/4 and every positive power lie inside it and outside the earlier Bundschuh-Vaananen region, while 3/2 lies outside both.
  • At n = 0, the Amdeberhan-Zeilberger q-Apery operator applied to Van Assche's moving diagonal has residual -p(p-1)^2(p+1)(p^5+2p^4+2p^3+2p^2+2), which is strictly negative and nonzero for every real p > 1.

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

locally proved result; novelty unassessed family: rational_base_tail_recurrence

The rational-base cleared tail obeys its exact first-order recurrence.

The recurrence is not derived from a rationality contradiction.

What is not checked

  • Irrationality at base three halves, or for any rational base.
  • The published analytic height theorem, which is cited and used as an external result and is not formalised here.
  • The all-scale Heine-Zudilin coefficient construction at rational base three halves; the primary source assumes an integer base.
  • The source analytic irrationality theorem inside the 81/200 height region; only its elementary parameter specialisations are formalised.
  • A sufficiently large primitive-normalised, non-collapsed coefficient family meeting the checked n >= 4R+2S threshold at the required quadratic depths.
  • That one of the resulting bounded-coefficient collision vectors has a nonzero polynomial pair, lies outside the analytic remainder nullspace, and has sufficient local gain.
  • Positivity or decay of the elementary Padé remainder; only its exponent arithmetic is checked.
  • Any general recurrence, endpoint, lattice, valuation, denominator, or irrationality conclusion from the n = 0 q-Apery residual; it proves only that the named scalar recurrence does not transfer to Van Assche's diagonal.

Open obligations

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

  • three_halves_growing_rank_endpoint_jet_kernel After dividing every coefficient pair by its rowwise common content, at positive quadratic target depths R_n,S_n exhibit at least 4R_n+2S_n primitive coefficient pairs from a genuinely non-collapsed deformation, prove that the required two-adic and three-adic gain survives primitive normalisation, and prove that at least one resulting checked {-1,0,1} collision has a nonzero polynomial pair and lies outside the analytic remainder nullspace; or prove an exact rank obstruction.

Lean modules

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 coordinatewise corridor forces a power-versus-linear inequality and cannot occur at base 3/2.

    This excludes one proof architecture and proves no irrationality statement.

    coordinatewise_corridor_no_go · targeted

  • The exact rational-base cleared-tail recurrence exposes exponential denominator-base forcing absent at integer bases.

    The recurrence is not derived from a rationality contradiction.

    rational_base_tail_recurrence · targeted

Represented indirectly

Covered through a neighbouring selected interface, not replayed one-to-one.

  • Integer scalar content changes analytic error and exterior determinant by matching factors, yielding no margin by itself.

    The conclusion is scoped to one normalisation strategy.

    scalar_content_no_go · represented_by_selected_coordinatewise_no_go

  • Endpoint residues at 2 and 3 exclude a common multiplier under unit-endpoint hypotheses.

    Other local or cross-row arithmetic remains possible.

    endpoint_residues · represented_by_selected_coordinatewise_no_go

Outside the Comparator selection

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

  • Binary selectors collide in the four-jet signature at the stated rank and depth.

    A signed relation is not nonzero analytic data.

    four_jet_collision · not_selected_finite_combinatorial_family

  • Irrationality at 7/2 is obtained from an external analytic criterion whose elementary height hypothesis is checked in Lean.

    Comparator may check the height inequality, not the cited theorem application.

    seven_halves_irrationality · not_applicable_to_external_irrationality_conclusion

  • Exact height-region inclusions and exclusions, Padé denominator-exponent bounds, and a rectangular Hermite-Padé threshold no-go are checked.

    The analytic remainder and nonvanishing input remain untreated.

    height_and_pade_arithmetic · not_selected_multiple_scoped_arithmetic_families

The paper

Problem note 24 pp

Arithmetic Boundaries at Base 3/2

At the resistant base 3/2, Lean rules out two common-width linear-form mechanisms: scalar content gives no net local-to-Archimedean gain, and unit endpoints exclude both 3 and 2 from a common divisor. A four-jet count constructs a signed relation but not a nonzero analytic remainder; direct cut-level clearing also incurs an exponential denominator factor and an impossible corridor inequality. The elementary 7/2 height bound is formalised, but the published analytic criterion remains external. These are construction-specific exclusions, not an irrationality result; Erdős #1049 remains open.