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Question 11444: An Indicator’s Measurability Depends on Its Event

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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R0021-11444 · q-20261013-advance-20261024-r02-measurable-function-0069

Original question and givens

Use complete qualified finite source and target sigma-algebras. Each subset has sorted distinct carrier labels; the duplicate-free family is already ordered by increasing bit mask. Check preimages of target measurable sets, not images of source sets. Measurable does not mean continuous, integrable or measure-preserving. source size=6, source sigma=[[], [0, 1, 4], [2, 3, 5], [0, 1, 2, 3, 4, 5]], event=[0] normalized as a set. The indicator maps members to 1 and others to 0, with the full measurable structure on {0,1}. Give (source size,event,complete indicator mapping,event is source-measurable?).

  • G001 — Use complete qualified finite source and target sigma-algebras. Each subset has sorted distinct carrier labels; the duplicate-free family is already ordered by increasing bit mask. Check preimages of target measurable sets, not images of source sets. Measurable does not mean continuous, integrable or measure-preserving. source size=6, source sigma=[[], [0, 1, 4], [2, 3, 5], [0, 1, 2, 3, 4, 5]], event=[0] normalized as a set. The indicator maps members to 1 and others to 0, with the full measurable structure on {0,1}. Give (source size,event,complete indicator mapping,event is source-measurable?).

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

indicator source:carrier Fin(6);complete canonical sigma family=[[], [0, 1, 4], [2, 3, 5], [0, 1, 2, 3, 4, 5]]

After

empty member=Yes;whole member=Yes;missing complements=[];missing pair unions=[]

Conditions: none

Qualify the complete bit-mask-ordered family:empty set,universe,complements and all pair unions.In a finite family a countable union has only finitely many distinct members,so finite-union closure suffices.

Step identifiers and dependencies

Rule: qualify_complete_finite_sigma_algebra · Uses: G001

S002 · implies

Before

source label=0;normalized event=[0]

After

indicator value=1

Conditions: none

Event members map to1;other source points map to0.The indicator's target is{0,1},not the source carrier.

Step identifiers and dependencies

Rule: indicator_one_on_event_zero_elsewhere · Uses: G001, S001

S003 · implies

Before

source label=1;normalized event=[0]

After

indicator value=0

Conditions: none

Event members map to1;other source points map to0.The indicator's target is{0,1},not the source carrier.

Step identifiers and dependencies

Rule: indicator_one_on_event_zero_elsewhere · Uses: G001, S002

S004 · implies

Before

source label=2;normalized event=[0]

After

indicator value=0

Conditions: none

Event members map to1;other source points map to0.The indicator's target is{0,1},not the source carrier.

Step identifiers and dependencies

Rule: indicator_one_on_event_zero_elsewhere · Uses: G001, S003

S005 · implies

Before

source label=3;normalized event=[0]

After

indicator value=0

Conditions: none

Event members map to1;other source points map to0.The indicator's target is{0,1},not the source carrier.

Step identifiers and dependencies

Rule: indicator_one_on_event_zero_elsewhere · Uses: G001, S004

S006 · implies

Before

source label=4;normalized event=[0]

After

indicator value=0

Conditions: none

Event members map to1;other source points map to0.The indicator's target is{0,1},not the source carrier.

Step identifiers and dependencies

Rule: indicator_one_on_event_zero_elsewhere · Uses: G001, S005

S007 · implies

Before

source label=5;normalized event=[0]

After

indicator value=0

Conditions: none

Event members map to1;other source points map to0.The indicator's target is{0,1},not the source carrier.

Step identifiers and dependencies

Rule: indicator_one_on_event_zero_elsewhere · Uses: G001, S006

S008 · implies

Before

event=[0];indicator mapping=[1, 0, 0, 0, 0, 0];target full sigma=[[],[0],[1],[0,1]]

After

preimages=[[],[1, 2, 3, 4, 5],[0],[0, 1, 2, 3, 4, 5]];event in source sigma=No

Conditions: none

The four target preimages are empty,event complement,event,and universe.The qualified source sigma contains empty/universe and is complement-closed,so indicator measurability is equivalent to event measurability.

Step identifiers and dependencies

Rule: indicator_all_four_preimages_equivalence · Uses: G001, S007

Reverse checks

  • S008 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S007 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S006 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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 — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(6, [0], [1, 0, 0, 0, 0, 0], No)

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: 7f089d9a5130cf0d8fffc588ef3119106ada0516049a032f7b47893ce3fe0107
  • candidate record SHA-256: 387e30c12193dec56617e102eb36456aed481f8c321848222f7014e03df1c09b
  • semantic review receipt SHA-256: 47d23d3735987d68e27733b051bdfa80a3616d44fb223b82bf2e6c8e46d49258
  • question-first witness SHA-256: a857db558000724020d2d5e815cb6bc3e2c9e2933df295bf33eb478d3c695139
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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