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Question 31749: A Common Divisor versus the Actual GCD

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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← Question derivation index · Original question batch

R0062-31749 · q-20261013-advance-20261018-r03-gcd-coprime-0049

Original question and givens

Natural numbers include 0. Every a divides 0; 0 divides b exactly when b=0. Divisibility witnesses are natural-number multipliers, not approximate quotients. a=128, b=162, candidate d=3; adopt gcd(0,0)=0. Give (a, b, d, d divides a?, d divides b?, d equals gcd?, gcd, both common-divisor and gcd qualifications?).

  • G001 — Natural numbers include 0. Every a divides 0; 0 divides b exactly when b=0. Divisibility witnesses are natural-number multipliers, not approximate quotients. a=128, b=162, candidate d=3; adopt gcd(0,0)=0. Give (a, b, d, d divides a?, d divides b?, d equals gcd?, gcd, both common-divisor and gcd qualifications?).

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 roles = [qf-ext18-gcd-common-divisor-audit, Nat_gcd, gcd-common-divisor-audit, no-form-field]

After

derived = [[a, b, d, divides_a, divides_b, equals_gcd, gcd, common_AND_gcd]]

Conditions: none

Check THIS bank interface:BASE equations use form/domain;BASE events/complement have no operation;factorials have no domain.ext18 uses local hyphens,other legacy operations underscores.Do not force every answer into a tuple or fraction.

Step identifiers and dependencies

Rule: R62_EXACT_source_keys_domain_operation_form_AND_output_types · Uses: G001

S002 · calculation

Before

GCD Euclid row0 ORIGINAL quotient times y := mul(0, 162)

After

GCD Euclid row0 ORIGINAL quotient times y = 0

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · calculation

Before

GCD Euclid row0 ORIGINAL x minus qy := sub(128, 0)

After

GCD Euclid row0 ORIGINAL x minus qy = 128

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · implies

Before

source roles = [128, 162, 0]

After

derived = [0, 128, [128, 162, 128]]

Conditions: none

With y≠0,divide to get x=qy+r and0≤r<y.A divisor common to x,y divides y,r,and the converse follows from x=qy+r,so common divisors are unchanged.Positive remainders strictly decrease,ensuring termination.

Step identifiers and dependencies

Rule: GCD_EUCLID_nonzero_divisor_exact_quotient_remainder_INVARIANT · Uses: G001, S003

S005 · calculation

Before

GCD Euclid row1 ORIGINAL quotient times y := mul(1, 128)

After

GCD Euclid row1 ORIGINAL quotient times y = 128

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S004

S006 · calculation

Before

GCD Euclid row1 ORIGINAL x minus qy := sub(162, 128)

After

GCD Euclid row1 ORIGINAL x minus qy = 34

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · implies

Before

source roles = [162, 128, 1]

After

derived = [128, 34, [162, 128, 34]]

Conditions: none

With y≠0,divide to get x=qy+r and0≤r<y.A divisor common to x,y divides y,r,and the converse follows from x=qy+r,so common divisors are unchanged.Positive remainders strictly decrease,ensuring termination.

Step identifiers and dependencies

Rule: GCD_EUCLID_nonzero_divisor_exact_quotient_remainder_INVARIANT · Uses: G001, S006

S008 · calculation

Before

GCD Euclid row2 ORIGINAL quotient times y := mul(3, 34)

After

GCD Euclid row2 ORIGINAL quotient times y = 102

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · calculation

Before

GCD Euclid row2 ORIGINAL x minus qy := sub(128, 102)

After

GCD Euclid row2 ORIGINAL x minus qy = 26

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S008

S010 · implies

Before

source roles = [128, 34, 3]

After

derived = [102, 26, [128, 34, 26]]

Conditions: none

With y≠0,divide to get x=qy+r and0≤r<y.A divisor common to x,y divides y,r,and the converse follows from x=qy+r,so common divisors are unchanged.Positive remainders strictly decrease,ensuring termination.

Step identifiers and dependencies

Rule: GCD_EUCLID_nonzero_divisor_exact_quotient_remainder_INVARIANT · Uses: G001, S009

S011 · calculation

Before

GCD Euclid row3 ORIGINAL quotient times y := mul(1, 26)

After

GCD Euclid row3 ORIGINAL quotient times y = 26

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S010

S012 · calculation

Before

GCD Euclid row3 ORIGINAL x minus qy := sub(34, 26)

After

GCD Euclid row3 ORIGINAL x minus qy = 8

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S011

S013 · implies

Before

source roles = [34, 26, 1]

After

derived = [26, 8, [34, 26, 8]]

Conditions: none

With y≠0,divide to get x=qy+r and0≤r<y.A divisor common to x,y divides y,r,and the converse follows from x=qy+r,so common divisors are unchanged.Positive remainders strictly decrease,ensuring termination.

Step identifiers and dependencies

Rule: GCD_EUCLID_nonzero_divisor_exact_quotient_remainder_INVARIANT · Uses: G001, S012

S014 · calculation

Before

GCD Euclid row4 ORIGINAL quotient times y := mul(3, 8)

After

GCD Euclid row4 ORIGINAL quotient times y = 24

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S013

S015 · calculation

Before

GCD Euclid row4 ORIGINAL x minus qy := sub(26, 24)

After

GCD Euclid row4 ORIGINAL x minus qy = 2

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S014

S016 · implies

Before

source roles = [26, 8, 3]

After

derived = [24, 2, [26, 8, 2]]

Conditions: none

With y≠0,divide to get x=qy+r and0≤r<y.A divisor common to x,y divides y,r,and the converse follows from x=qy+r,so common divisors are unchanged.Positive remainders strictly decrease,ensuring termination.

Step identifiers and dependencies

Rule: GCD_EUCLID_nonzero_divisor_exact_quotient_remainder_INVARIANT · Uses: G001, S015

S017 · calculation

Before

GCD Euclid row5 ORIGINAL quotient times y := mul(4, 2)

After

GCD Euclid row5 ORIGINAL quotient times y = 8

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S016

S018 · calculation

Before

GCD Euclid row5 ORIGINAL x minus qy := sub(8, 8)

After

GCD Euclid row5 ORIGINAL x minus qy = 0

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S017

S019 · implies

Before

source roles = [8, 2, 4]

After

derived = [8, 0, [8, 2, 0]]

Conditions: none

With y≠0,divide to get x=qy+r and0≤r<y.A divisor common to x,y divides y,r,and the converse follows from x=qy+r,so common divisors are unchanged.Positive remainders strictly decrease,ensuring termination.

Step identifiers and dependencies

Rule: GCD_EUCLID_nonzero_divisor_exact_quotient_remainder_INVARIANT · Uses: G001, S018

S020 · implies

Before

source roles = [128, 162, [[128, 162, 128], [162, 128, 34], [128, 34, 26], [34, 26, 8], [26, 8, 2], [8, 2, 0]]]

After

derived = [2, 0]

Conditions: none

At second value0 retain the last x.For nonzero x,gcd(x,0)=x;the two-way common-divisor invariant transfers this to the original pair.At(0,0)use the EXPLICIT convention gcd=0,not a claim that0 is the largest positive divisor.

Step identifiers and dependencies

Rule: GCD_TERMINAL_last_x_ZEROsecond_and_explicit_gcd00_convention · Uses: G001, S019

S021 · implies

Before

source roles = [GCD candidate divides a, 3, 128]

After

derived = [No, not-applicable]

Conditions: none

Natural divisibility at d=0 holds ONLY for x=0;choose multiplier0 for0∣0 without claiming uniqueness.For nonzero d,show a multiplier ONLY at remainder0.Two divisibility flags alone do not establish greatestness.

Step identifiers and dependencies

Rule: GCD_DIVISIBILITY_ZERO_guard_before_natural_multiplier · Uses: G001, S020

S022 · calculation

Before

GCD candidate divides b ORIGINAL exact multiplier := div(162, 3)

After

GCD candidate divides b ORIGINAL exact multiplier = 54

Conditions: none

Use ORIGINAL operands and declared order for exact integer/rational arithmetic,not floats.Bounds are family-specific:do not revalidate derived values as RAW inputs or add blanket SAFE/n64 caps to BASE families.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S021

S023 · implies

Before

source roles = [GCD candidate divides b, 3, 162]

After

derived = [Yes, 54]

Conditions: none

Natural divisibility at d=0 holds ONLY for x=0;choose multiplier0 for0∣0 without claiming uniqueness.For nonzero d,show a multiplier ONLY at remainder0.Two divisibility flags alone do not establish greatestness.

Step identifiers and dependencies

Rule: GCD_DIVISIBILITY_ZERO_guard_before_natural_multiplier · Uses: G001, S022

S024 · implies

Before

source roles = [128, 162, 3, 2]

After

derived = [No, Yes, No, 2, No]

Conditions: none

FIRST compute the actual gcd from ORIGINAL a,b independently of candidate d.A common divisor need not be greatest.Keep d∣a,d∣b,d=gcd,and their conjunction SEPARATE.

Step identifiers and dependencies

Rule: GCD_AUDIT_actual_gcd_INDEPENDENT_of_candidate_common_AND_greatest · Uses: G001, S023

Reverse checks

  • S024 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S023 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S022 · premise_and_result_audit — Recompute GCD candidate divides b ORIGINAL exact multiplier with exact rational arithmetic, not rounded decimals.
  • S021 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S020 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S019 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S018 · premise_and_result_audit — Recompute GCD Euclid row5 ORIGINAL x minus qy with exact rational arithmetic, not rounded decimals.
  • S017 · premise_and_result_audit — Recompute GCD Euclid row5 ORIGINAL quotient times y with exact rational arithmetic, not rounded decimals.
  • S016 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S015 · premise_and_result_audit — Recompute GCD Euclid row4 ORIGINAL x minus qy with exact rational arithmetic, not rounded decimals.
  • S014 · premise_and_result_audit — Recompute GCD Euclid row4 ORIGINAL quotient times y with exact rational arithmetic, not rounded decimals.
  • S013 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S012 · premise_and_result_audit — Recompute GCD Euclid row3 ORIGINAL x minus qy with exact rational arithmetic, not rounded decimals.
  • S011 · premise_and_result_audit — Recompute GCD Euclid row3 ORIGINAL quotient times y with exact rational arithmetic, not rounded decimals.
  • S010 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S009 · premise_and_result_audit — Recompute GCD Euclid row2 ORIGINAL x minus qy with exact rational arithmetic, not rounded decimals.
  • S008 · premise_and_result_audit — Recompute GCD Euclid row2 ORIGINAL quotient times y with exact rational arithmetic, not rounded decimals.
  • S007 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S006 · premise_and_result_audit — Recompute GCD Euclid row1 ORIGINAL x minus qy with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Recompute GCD Euclid row1 ORIGINAL quotient times y with exact rational arithmetic, not rounded decimals.
  • S004 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.
  • S003 · premise_and_result_audit — Recompute GCD Euclid row0 ORIGINAL x minus qy with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Recompute GCD Euclid row0 ORIGINAL quotient times y with exact rational arithmetic, not rounded decimals.
  • S001 · premise_and_result_audit — Reverse-check the ORIGINAL inputs,field roles,domain and premises.Consistency does not imply unique recovery of premises.Keep finite checking,independent review,formal proof and publication separate.

Result

(128, 162, 3, No, Yes, No, 2, 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: b1159a17f4845acebfdcd2899388af427f4273db52349b7a55d15acd6140eccc
  • candidate record SHA-256: 2f72adeeefa8e34b7bb0e19b66c25a94ccfd6ca83f6a1753052cb1f41307389a
  • semantic review receipt SHA-256: 963099ffc9f754069fdce6792949a85ed350472465eaceb3038fa8011cf672bd
  • question-first witness SHA-256: d7655324c5d11528e1af90b757384cebd3313e19dc5f6f5b9b8ea7624fb06f6f
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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