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Question 20338: A Smaller Domain Does Not Generally Decide the Given Map Is Injective

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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R0039-20338 · q-20261014-advance-20261107-r05-pigeonhole-principle-0088

Original question and givens

Use the complete total mapping=[0, 0, 2, 3, 4] from source indices Fin(5)={0,…,4} into Fin(8)={0,…,7}. The codomain is nonempty; every source has exactly one in-range image. Compute full fibre loads and collisions, not a sample. Domain size is at most codomain size. Give (domain_count, codomain_count, given_map_injective, general_reverse_implication_claim, boundary).

  • G001 — Use the complete total mapping=[0, 0, 2, 3, 4] from source indices Fin(5)={0,…,4} into Fin(8)={0,…,7}. The codomain is nonempty; every source has exactly one in-range image. Compute full fibre loads and collisions, not a sample. Domain size is at most codomain size. Give (domain_count, codomain_count, given_map_injective, general_reverse_implication_claim, 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=pigeon-converse-boundary;original snapshot and mathematics retained

After

explicit ordered source output fields=[domain_count, codomain_count, given_map_injective, general_reverse_implication_claim, boundary]

Conditions: none

Retain the historical interface marker in the original snapshot while listing ordered source fields here,without JavaScript or external lookup.Field labels are not additional mathematical evidence,and No retains the source claim scope.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

ORIGINAL complete source-indexed total map=[0, 0, 2, 3, 4];source Fin(5);ACTUAL target Fin(8)

After

every source has ONE in-range image;all target labels0..7 retained even if unused;empty source allowed

Conditions: none

Retain original source order and target labels rather than relabeling bins by first appearance.Complete total-map data support full fibres and collisions,including an empty source into a nonempty codomain.

Step identifiers and dependencies

Rule: pigeon_complete_total_map_not_sample_or_bin_relabeling · Uses: G001, S001

S003 · implies

Before

next LEX ordered original source pair=[0, 1] with left<right;original images=[0, 0]

After

same target image=Yes;every earlier LEFT-then-RIGHT pair already checked unequal

Conditions: none

Check left first and then right;the first equal pair is the source's first lexicographic pair,which may differ from the earliest repeat encountered by increasing right endpoint.

Step identifiers and dependencies

Rule: pigeon_first_collision_lex_pair_not_first_repeat_stream · Uses: G001, S002

S004 · implies

Before

ACTUAL original source size=5<=target size=8;complete-map first collision=[0, 1, 0]

After

GIVEN map injective=No;GENERAL reverse-implication claim=No;these are different fields

Conditions: none

Injectivity comes from all pairs of this complete map and may be true or false.The final No only withholds the general reverse inference;it does not force empty,singleton or other injective maps to false.

Step identifiers and dependencies

Rule: pigeon_given_map_injective_separate_from_general_nonclaim · Uses: G001, S003

Reverse checks

  • 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

(5, 8, No, No, size_condition_failure_does_not_imply_given_map_is_injective)

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: 0d24315117ee2d56e92aa5652542c5afca0ab5e75bcfdae9c47656f0de277d48
  • candidate record SHA-256: 8f6e743ae50154d5c2d103e7497a6101afed03671a4d7e36c3dde779ff5ec05c
  • semantic review receipt SHA-256: 6e11e35fafe32f16900ce9b522d01acb7b2ee6b463ab179392076cfbe1af8034
  • question-first witness SHA-256: cc0fa361fc25151729e70264340d2eae94f179f6f2a2edfe80ba5704fbbd0682
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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