# Question 26232: The Geometric Tail Bound Controls the Exact Picard Error

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This teaching derivation has second-context AI mathematical and bilingual semantic review, limited to the model and assumptions stated in this question. It has no human review or new Lean proof and does not promote the original question or MKO to Canonical truth.

R0051-26232 · q-20261015-advance-20261116-r01-contraction-mapping-theorem-0057



## Original question and givens

Use the complete exact metric matrix=[[0, 7, 21], [7, 0, 14], [21, 14, 0]], aligned mapping=[0, 0, 1] and q=1/2. Qualify nonnegativity, separation, symmetry and every triangle, the entire self-map and every ordered contraction pair. A finite metric space is complete. Start=2, steps=3. Give (orbit, fixed_point, actual_error, geometric_bound, bound_holds, certificate).


- G001 — Use the complete exact metric matrix=[[0, 7, 21], [7, 0, 14], [21, 14, 0]], aligned mapping=[0, 0, 1] and q=1/2. Qualify nonnegativity, separation, symmetry and every triangle, the entire self-map and every ordered contraction pair. A finite metric space is complete. Start=2, steps=3. Give (orbit, fixed_point, actual_error, geometric_bound, bound_holds, certificate).





## 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.


- [mko-contraction-mapping-theorem](https://ocme.evemisslab.com/en/mko/mko-contraction-mapping-theorem/)





## Step-by-step derivation

S001 · impliesBefore

source roles = [contract-fixed-point-bound]

After

derived = [[orbit, fixed_point, actual_error, geometric_bound, bound_holds, certificate]]

Conditions: none

List the full source field order without JavaScript.Original modes select contract6/4/6/6 and IVT8/7/8 roles,without padding or answer-shape inference.

Step identifiers and dependenciesRule: source_ordered_fields_without_JS · Uses: G001





S002 · impliesBefore

source roles = [[[0, 7, 21], [7, 0, 14], [21, 14, 0]]]

After

derived = [3, Yes, Yes, Yes, [[0, 0, 0, 0, 0, Yes], [0, 0, 1, 7, 7, Yes], [0, 0, 2, 21, 21, Yes], [0, 1, 0, 0, 14, Yes], [0, 1, 1, 7, 7, Yes], [0, 1, 2, 21, 21, Yes], [0, 2, 0, 0, 42, Yes], [0, 2, 1, 7, 35, Yes], [0, 2, 2, 21, 21, Yes], [1, 0, 0, 7, 7, Yes], [1, 0, 1, 0, 14, Yes], [1, 0, 2, 14, 28, Yes], [1, 1, 0, 7, 7, Yes], [1, 1, 1, 0, 0, Yes], [1, 1, 2, 14, 14, Yes], [1, 2, 0, 7, 35, Yes], [1, 2, 1, 0, 28, Yes], [1, 2, 2, 14, 14, Yes], [2, 0, 0, 21, 21, Yes], [2, 0, 1, 14, 28, Yes], [2, 0, 2, 0, 42, Yes], [2, 1, 0, 21, 21, Yes], [2, 1, 1, 14, 14, Yes], [2, 1, 2, 0, 28, Yes], [2, 2, 0, 21, 21, Yes], [2, 2, 1, 14, 14, Yes], [2, 2, 2, 0, 0, Yes]], Yes]

Conditions: none

Check every triangle triple,not sampled metric behavior.A nonempty finite metric is complete:trivial for a singleton;otherwise the minimum positive distance delta forces a Cauchy tail with distances<delta to be constant,with limit in X.

Step identifiers and dependenciesRule: Contraction_COMPLETE_metric_axioms_ALL_triangles_finite_completeness · Uses: G001, S001





S003 · calculationBefore

Contraction ORIGINAL pair0,0 q times distance := mul(1/2, 0)

After

Contraction ORIGINAL pair0,0 q times distance = 0

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S002





S004 · calculationBefore

Contraction ORIGINAL pair0,1 q times distance := mul(1/2, 7)

After

Contraction ORIGINAL pair0,1 q times distance = 7/2

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S003





S005 · calculationBefore

Contraction ORIGINAL pair0,2 q times distance := mul(1/2, 21)

After

Contraction ORIGINAL pair0,2 q times distance = 21/2

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S004





S006 · calculationBefore

Contraction ORIGINAL pair1,0 q times distance := mul(1/2, 7)

After

Contraction ORIGINAL pair1,0 q times distance = 7/2

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S005





S007 · calculationBefore

Contraction ORIGINAL pair1,1 q times distance := mul(1/2, 0)

After

Contraction ORIGINAL pair1,1 q times distance = 0

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S006





S008 · calculationBefore

Contraction ORIGINAL pair1,2 q times distance := mul(1/2, 14)

After

Contraction ORIGINAL pair1,2 q times distance = 7

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S007





S009 · calculationBefore

Contraction ORIGINAL pair2,0 q times distance := mul(1/2, 21)

After

Contraction ORIGINAL pair2,0 q times distance = 21/2

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S008





S010 · calculationBefore

Contraction ORIGINAL pair2,1 q times distance := mul(1/2, 14)

After

Contraction ORIGINAL pair2,1 q times distance = 7

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S009





S011 · calculationBefore

Contraction ORIGINAL pair2,2 q times distance := mul(1/2, 0)

After

Contraction ORIGINAL pair2,2 q times distance = 0

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S010





S012 · impliesBefore

source roles = [[0, 0, 1], 1/2, [[0, 7, 21], [7, 0, 14], [21, 14, 0]]]

After

derived = [Yes, Yes, [[0, 0, 0, 0, Yes], [0, 1, 0, 7/2, Yes], [0, 2, 7, 21/2, Yes], [1, 0, 0, 7/2, Yes], [1, 1, 0, 0, Yes], [1, 2, 7, 7, Yes], [2, 0, 7, 21/2, Yes], [2, 1, 7, 7, Yes], [2, 2, 0, 0, Yes]], Yes, [0]]

Conditions: none

Separate self-map,0<=q<1 and all pair inequalities.Nonself maps have empty source pair rows;self maps retain actual pair results even when q-range fails.Array length or samples do not prove global contraction.

Step identifiers and dependenciesRule: Contraction_selfmap_q_range_ALL_ordered_pairs_separate · Uses: G001, S011





S013 · impliesBefore

source roles = [0, 2, [0, 0, 1]]

After

derived = [1, 7]

Conditions: none

Apply the same complete map at every step,retaining the start and all iterates rather than guessing a fixed point from a short prefix.

Step identifiers and dependenciesRule: Contraction_EACH_Picard_iterate_original_total_map · Uses: G001, S012





S014 · impliesBefore

source roles = [1, 1, [0, 0, 1]]

After

derived = [0, 0]

Conditions: none

Apply the same complete map at every step,retaining the start and all iterates rather than guessing a fixed point from a short prefix.

Step identifiers and dependenciesRule: Contraction_EACH_Picard_iterate_original_total_map · Uses: G001, S013





S015 · impliesBefore

source roles = [2, 0, [0, 0, 1]]

After

derived = [0, 0]

Conditions: none

Apply the same complete map at every step,retaining the start and all iterates rather than guessing a fixed point from a short prefix.

Step identifiers and dependenciesRule: Contraction_EACH_Picard_iterate_original_total_map · Uses: G001, S014





S016 · impliesBefore

source roles = [1/2, [0], 2, [2, 1, 0, 0]]

After

derived = [[21, 7, 0, 0], d(x_(n+k),x_n)<=q^n*(1-q^k)/(1-q)*d(x1,x0), complete limit fixed;two fixed points obey(1-q)d<=0 hence coincide]

Conditions: none

Successive distances shrink by q;the triangle inequality sums the finite geometric tail,making Picard Cauchy.Completeness gives a limit and Lipschitz continuity makes it fixed.Two fixed points satisfy distance<=q*distance,so q<1 forces equality.This pedagogical argument does not label a finite orbit a general formal proof.

Step identifiers and dependenciesRule: Contraction_GENERAL_geometric_tail_complete_limit_and_unique_fixed · Uses: G001, S015





S017 · impliesBefore

(1/2)^3

After

Contraction ORIGINAL q powerN = 1/8

Conditions: none

Evaluate the finite nonnegative-integer power exactly; exponent0 uses the polynomial multiplicative identity.

Step identifiers and dependenciesRule: integer_power · Uses: G001, S016





S018 · calculationBefore

Contraction strict one minus q := sub(1, 1/2)

After

Contraction strict one minus q = 1/2

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S017





S019 · calculationBefore

Contraction geometric tail factor := div(1/8, 1/2)

After

Contraction geometric tail factor = 1/4

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S018





S020 · calculationBefore

Contraction factor times ORIGINAL first-step distance := mul(1/4, 14)

After

Contraction factor times ORIGINAL first-step distance = 7/2

Conditions: none

Substitute original roles and established intermediates exactly,without rounding;extra teaching identities do not restrict the source domain.

Step identifiers and dependenciesRule: exact_rational_arithmetic · Uses: G001, S019





S021 · impliesBefore

source roles = [3, 1/2, [2, 1, 0, 0], 0, 14]

After

derived = [0, 7/2, Yes]

Conditions: none

Let tail length tend to infinity to obtain the error bound.At N0,q^0 is the empty product1,including q0.The source computes powers/division before multiplying first distance;zero distance does not bypass its numeric profile.

Step identifiers and dependenciesRule: Contraction_actual_error_bound_N0_q0_profile_NOT_shortcircuited · Uses: G001, S020









## Reverse checks


- S021 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S020 · premise_and_result_audit — Recompute Contraction factor times ORIGINAL first-step distance with exact rational arithmetic, not rounded decimals.
- S019 · premise_and_result_audit — Recompute Contraction geometric tail factor with exact rational arithmetic, not rounded decimals.
- S018 · premise_and_result_audit — Recompute Contraction strict one minus q with exact rational arithmetic, not rounded decimals.
- S017 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S016 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S015 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S014 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S013 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S012 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
- S011 · premise_and_result_audit — Recompute Contraction ORIGINAL pair2,2 q times distance with exact rational arithmetic, not rounded decimals.
- S010 · premise_and_result_audit — Recompute Contraction ORIGINAL pair2,1 q times distance with exact rational arithmetic, not rounded decimals.
- S009 · premise_and_result_audit — Recompute Contraction ORIGINAL pair2,0 q times distance with exact rational arithmetic, not rounded decimals.
- S008 · premise_and_result_audit — Recompute Contraction ORIGINAL pair1,2 q times distance with exact rational arithmetic, not rounded decimals.
- S007 · premise_and_result_audit — Recompute Contraction ORIGINAL pair1,1 q times distance with exact rational arithmetic, not rounded decimals.
- S006 · premise_and_result_audit — Recompute Contraction ORIGINAL pair1,0 q times distance with exact rational arithmetic, not rounded decimals.
- S005 · premise_and_result_audit — Recompute Contraction ORIGINAL pair0,2 q times distance with exact rational arithmetic, not rounded decimals.
- S004 · premise_and_result_audit — Recompute Contraction ORIGINAL pair0,1 q times distance with exact rational arithmetic, not rounded decimals.
- S003 · premise_and_result_audit — Recompute Contraction ORIGINAL pair0,0 q times distance with exact rational arithmetic, not rounded decimals.
- 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

([2, 1, 0, 0], 0, 0, 7/2, Yes, d_xn_fixed_le_qn_over_one_minus_q_times_d_x1_x0)

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: 3b5bdd0526b0d5d43a33577c892612c867c29e7a23372bc99320e654bad880f9
- candidate record SHA-256: 06a335f0c9e7430f31a539cb20f010012dae508252dd06813eb40975a93f548b
- semantic review receipt SHA-256: 90df1e889242e9afdf01e068788ee8500ef366ffcfc0496e30a6800de32631c3
- question-first witness SHA-256: ae1e849608590ca856c9f3b6911ba58e3bf53c608eb7369606192a770f48bd5c
- Lean: NOT_RUN · human review: NOT_PERFORMED

[Same-source full JSON](https://ocme.evemisslab.com/data/question-derivations/questions/q-20261015-advance-20261116-r01-contraction-mapping-theorem-0057.json)




