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Question 22851: Continuous and Atomless Does Not Imply a Density

On this page
  1. Original question and givens
  2. Definition and scope
  3. Step-by-step derivation
  4. Reverse checks
  5. Result
  6. This question review and source binding

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R0044-22851 · q-20261014-advance-20261111-r04-continuous-real-distribution-function-0076

Original question and givens

Use the standard Cantor distribution affinely carried onto [-1,2], with left<right. Give (left, right, CDF_continuous, atomless, has_density, singular, boundary).

  • G001 — Use the standard Cantor distribution affinely carried onto [-1,2], with left<right. Give (left, right, CDF_continuous, atomless, has_density, singular, boundary).

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

Step-by-step derivation

S001 · implies

Before

source operation=contcdf-singular-no-density-boundary;original snapshot and mathematics retained

After

explicit ordered source output fields=[left, right, CDF_continuous, atomless, has_density, singular, boundary]

Conditions: none

Keep the historical interface marker and list ordered source fields without JavaScript.Tags are not additional evidence;fixed No markers retain their scope.The ordering helper supplies protocol order,not mathematical correctness.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · calculation

Before

Cantor affine support positive width := sub(2, -1)

After

Cantor affine support positive width = 3

Conditions: none

Substitute original roles,indices and established intermediates exactly,not floating-point approximations or another question's data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · implies

Before

ORIGINAL affine Cantor support[-1,2];positive width W=3

After

take independent fair digits B_k in{0,1},Y=sum_(k>=1)2*B_k/3^k and X=L+W*Y;the geometric tail converges and X lies in the affine Cantor support

Conditions: none

This defines the whole Cantor law,not the piecewise-linear constructor or a finite CDF sample.The convergent ternary0/2 series has probability1 on Cantor support,and the positive affine transformation is nondegenerate.

Step identifiers and dependencies

Rule: contcdf_Cantor_WHOLE_binary_digit_construction_not_knots · Uses: G001, S002

S004 · implies

Before

ORIGINAL support width W=3;level n ternary construction uses2^n intervals of length W/3^n

After

total level-n length=W*(2/3)^n tends0,so support has Lebesgue measure0;any singleton has probability<=2*2^(-n) for EVERY n,hence atom probability0;CDF jumps are0

Conditions: none

The nested level sets contain the support and their total length tends0,proving Lebesgue-null support.A fixed point is bounded by at most two relevant cylinder masses2^(-n).The bound for every n proves no atoms,not sampling finitely many points.

Step identifiers and dependencies

Rule: contcdf_Cantor_null_support_and_vanishing_atom_bounds · Uses: G001, S003

S005 · implies

Before

ORIGINAL affine law on[-1,2] has support N with Lebesgue measure0 and probability1;all singleton probabilities0

After

CDF_continuous=Yes;atomless=Yes;has_density=No;singular=Yes;any Lebesgue density would integrate to0 over N,contradicting probability1

Conditions: none

CDF jumps equal singleton masses;an everywhere atomless law has a continuous CDF.The full-probability null support proves singularity and rules out a Lebesgue density,since its integral over that support would be0.This is a particular counterexample to continuity/atomlessness implying density.

Step identifiers and dependencies

Rule: contcdf_Cantor_continuous_atomless_singular_NO_density · Uses: G001, S004

Reverse checks

  • S005 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S004 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S003 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S002 · premise_and_result_audit — Recompute Cantor affine support positive width with exact rational arithmetic, not rounded decimals.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(-1, 2, Yes, Yes, No, Yes, affine_Cantor_distribution_is_continuous_atomless_and_singular_without_a_density)

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.

Source hashes and review receipts
  • input commit: 0f7be61e2c22317a4075561dc822c87d881a50db
  • original question SHA-256: 3064b8c3f8fad47d40404655efc3d830dbfafca28f4aaff9c18bdf2ec5b007c5
  • candidate record SHA-256: 2d335bc531a707a52f4f67208dcc89b9555828ef90a35476d4809a6b739d21b4
  • semantic review receipt SHA-256: 89b8e810eced1a69dbfef28d4b112e829edf156c7905a86e39a3f4958cd75e81
  • question-first witness SHA-256: b2e8b769c463242f05172564ae96e310403eae151e1ec30bcb50be3ffe12cfc7
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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