Question 11173: Linear Halfspace Closure at Qualified Endpoints

Original question and givens

Convexity means every pair of set members and every lambda in [0,1] has lambda*left+(1−lambda)*right in the set. Positive cases use complete algebraic certificates, not sampled lambda values. One exact counterexample suffices to refute convexity; a failed counterexample does not prove convexity. normal=[1, 1], bound=24, left=[0, 0], right=[23, 0], lambda=23/25∈[0,1]. Both endpoints must satisfy normal·point≤bound. Give (normal,bound,left,right,left dot product,right dot product,lambda,weighted point,its dot product,inside?). Use exact rational arithmetic, reduce fractions to positive denominators and omit /1 for integer outputs.

• G001 — Convexity means every pair of set members and every lambda in [0,1] has lambda*left+(1−lambda)*right in the set. Positive cases use complete algebraic certificates, not sampled lambda values. One exact counterexample suffices to refute convexity; a failed counterexample does not prove convexity. normal=[1, 1], bound=24, left=[0, 0], right=[23, 0], lambda=23/25∈[0,1]. Both endpoints must satisfy normal·point≤bound. Give (normal,bound,left,right,left dot product,right dot product,lambda,weighted point,its dot product,inside?). Use exact rational arithmetic, reduce fractions to positive denominators and omit /1 for integer outputs.

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-convex-set

Step-by-step derivation

left endpoint dot term0 := mul(1, 0)

left endpoint dot term0 = 0

left endpoint dot term1 := mul(1, 0)

left endpoint dot term1 = 0

left endpoint dot sum := sum(0, 0)

left endpoint dot sum = 0

right endpoint dot term0 := mul(1, 23)

right endpoint dot term0 = 23

right endpoint dot term1 := mul(1, 0)

right endpoint dot term1 = 0

right endpoint dot sum := sum(23, 0)

right endpoint dot sum = 23

normal=[1, 1];bound=24;left dot=0;right dot=23

both endpoints satisfy the closed halfspace inequality

halfspace point complementary weight := sub(1, 23/25)

halfspace point complementary weight = 2/25

halfspace point:raw lambda=[23, 25];lambda=23/25;one-minus-lambda=2/25

in_closed_unit_interval=Yes;lambda weights left

halfspace point:ordered vectors=[[0, 0], [23, 0]];aligned weights=[23/25, 2/25]

dimension=2;preserve duplicates and order

halfspace point coordinate0 term0 := mul(23/25, 0)

halfspace point coordinate0 term0 = 0

halfspace point coordinate0 term1 := mul(2/25, 23)

halfspace point coordinate0 term1 = 46/25

halfspace point coordinate0 sum := sum(0, 46/25)

halfspace point coordinate0 sum = 46/25

halfspace point coordinate1 term0 := mul(23/25, 0)

halfspace point coordinate1 term0 = 0

halfspace point coordinate1 term1 := mul(2/25, 0)

halfspace point coordinate1 term1 = 0

halfspace point coordinate1 sum := sum(0, 0)

halfspace point coordinate1 sum = 0

combined point dot term0 := mul(1, 46/25)

combined point dot term0 = 46/25

combined point dot term1 := mul(1, 0)

combined point dot term1 = 0

combined point dot sum := sum(46/25, 0)

combined point dot sum = 46/25

halfspace bound slack := sub(24, 46/25)

halfspace bound slack = 554/25

normal dot z=46/25;endpoint dots=(0,23);lambda=23/25;bound=24

normal dot z=lambda*0+(1-lambda)*23<=24;inside=Yes

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 halfspace bound slack with exact rational arithmetic, not rounded decimals.
• S019 · premise_and_result_audit — Recompute combined point dot sum with exact rational arithmetic, not rounded decimals.
• S018 · premise_and_result_audit — Recompute combined point dot term1 with exact rational arithmetic, not rounded decimals.
• S017 · premise_and_result_audit — Recompute combined point dot term0 with exact rational arithmetic, not rounded decimals.
• S016 · premise_and_result_audit — Recompute halfspace point coordinate1 sum with exact rational arithmetic, not rounded decimals.
• S015 · premise_and_result_audit — Recompute halfspace point coordinate1 term1 with exact rational arithmetic, not rounded decimals.
• S014 · premise_and_result_audit — Recompute halfspace point coordinate1 term0 with exact rational arithmetic, not rounded decimals.
• S013 · premise_and_result_audit — Recompute halfspace point coordinate0 sum with exact rational arithmetic, not rounded decimals.
• S012 · premise_and_result_audit — Recompute halfspace point coordinate0 term1 with exact rational arithmetic, not rounded decimals.
• S011 · premise_and_result_audit — Recompute halfspace point coordinate0 term0 with exact rational arithmetic, not rounded decimals.
• S010 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S009 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S008 · premise_and_result_audit — Recompute halfspace point complementary weight with exact rational arithmetic, not rounded decimals.
• 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 — Recompute right endpoint dot sum with exact rational arithmetic, not rounded decimals.
• S005 · premise_and_result_audit — Recompute right endpoint dot term1 with exact rational arithmetic, not rounded decimals.
• S004 · premise_and_result_audit — Recompute right endpoint dot term0 with exact rational arithmetic, not rounded decimals.
• S003 · premise_and_result_audit — Recompute left endpoint dot sum with exact rational arithmetic, not rounded decimals.
• S002 · premise_and_result_audit — Recompute left endpoint dot term1 with exact rational arithmetic, not rounded decimals.
• S001 · premise_and_result_audit — Recompute left endpoint dot term0 with exact rational arithmetic, not rounded decimals.

Result

([1, 1], 24, [0, 0], [23, 0], 0, 23, 23/25, [46/25, 0], 46/25, Yes)

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.