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Measure theory 1.2.4: require nonempty sets in dist_of_disj_compact_pos#540

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Chessing234:fix/measure-1-2-1-dist-nonempty
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Measure theory 1.2.4: require nonempty sets in dist_of_disj_compact_pos#540
Chessing234 wants to merge 1 commit into
teorth:mainfrom
Chessing234:fix/measure-1-2-1-dist-nonempty

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@Chessing234 Chessing234 commented Jun 24, 2026

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Summary

  • dist_of_disj_compact_pos claimed set_dist E F > 0 for any disjoint compact sets, but fails when either set is empty.

Root cause

set_dist E F = sInf (dist '' (E ×ˢ F)). For E = ∅, the image is empty and sInf ∅ = 0, contradicting > 0. Empty sets are compact and disjoint from anything.

Fix

Require E.Nonempty and F.Nonempty.

Test plan

  • lake build passes

Empty compact sets make set_dist 0 via sInf of an empty set, contradicting > 0.

Co-authored-by: Cursor <cursoragent@cursor.com>
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