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Question 413: Exact Binomial Coefficients Keep k and n Minus k Distinct

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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P1000-0413 · q-20261014-advance-20261109-r05-binomial-theorem-0013

Original question and givens

Use integer n=12 with 0≤n≤50 and integer k=12 with 0≤k≤n. The coefficient setting has commutative multiplication. Give (n, k, coefficient, symmetric_coefficient, equal).

  • G001 — Use integer n=12 with 0≤n≤50 and integer k=12 with 0≤k≤n. The coefficient setting has commutative multiplication. Give (n, k, coefficient, symmetric_coefficient, equal).

Definition and scope

Integer counting with 0≤k≤n. C(n,k) counts k-position subsets; the complement bijection gives symmetry.

Step-by-step derivation

S001 · implies

Before

n=12≥0; multiplication commutes

After

group the finite product by the number of y choices

Conditions: none

Choose x or y in each factor and group by the number of y choices; count coefficients as integers first.

Step identifiers and dependencies

Rule: commutative_product · Uses: G001

S002 · implies

Before

choose 12 positions out of 12

After

C(12,12)=479001600/(479001600·1)=1

Conditions: none

Count each k-position subset once, dividing out reorderings inside each of the two groups.

Step identifiers and dependencies

Rule: subset_count · Uses: G001, S001

S003 · implies

Before

choose 0 positions out of 12

After

C(12,0)=479001600/(1·479001600)=1

Conditions: none

Count each k-position subset once, dividing out reorderings inside each of the two groups.

Step identifiers and dependencies

Rule: subset_count · Uses: G001, S002

S004 · implies

Before

choose subset of size 12

After

its complement has size 0

Conditions: none

Taking complements is an invertible map, so the two counts agree.

Step identifiers and dependencies

Rule: subset_complement_bijection · Uses: G001, S003

S005 · implies

Before

C(12,12)=1; C(12,0)=1

After

symmetric coefficients equal: Yes

Conditions: none

The values agree with the complement bijection; n=0 still has exactly the empty subset.

Step identifiers and dependencies

Rule: coefficient_symmetry · Uses: G001, S004

Reverse checks

  • S005 · premise_and_result_audit — Count coefficients in the integers first; do not invert possibly nonunit factorials in a general coefficient ring.
  • S004 · premise_and_result_audit — Count coefficients in the integers first; do not invert possibly nonunit factorials in a general coefficient ring.
  • S003 · premise_and_result_audit — Count coefficients in the integers first; do not invert possibly nonunit factorials in a general coefficient ring.
  • S002 · premise_and_result_audit — Count coefficients in the integers first; do not invert possibly nonunit factorials in a general coefficient ring.
  • S001 · premise_and_result_audit — Count coefficients in the integers first; do not invert possibly nonunit factorials in a general coefficient ring.

Result

(12, 12, 1, 1, Yes)

The full substitutions and premise audits recover the original answer, retaining its field order and verdict meanings.

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: 51e2c4492d6f2acc7850ba21224b65152b02c1ff9e1d999334532df33ece3704
  • candidate record SHA-256: 3ac06b12151e3e0e5b92790dbfd2da6dcdfc414a49e817d52de8a526f4d0c1be
  • semantic review receipt SHA-256: 6c2c6d46aded7582a11ac41a8c0b3bdde2669a53bdb6e796eea2039994a02772
  • question-first witness SHA-256: 77e43898df9efdbf8094ad81fe4ab91cf4b4bd82f481eb9b4699b73cb4da612b
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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