Gallai’s conjecture on certain families of bipartite graphs
For every connected graph with vertices, the edges of admit a decomposition into at most paths.
References
Primary source
Additional references
- Gallai’s Conjecture on Certain Families of Bipartite Graphs — La Matematica — Akankshya Sahu, Sajith Padinhatteeri
Progress summary
A published paper reports progress for some bipartite graph families, but the general conjecture and the point–triple cases remain unsettled.
Gallai’s conjecture asks whether every connected graph can have its edges partitioned into at most half its vertices’ worth of paths, rounded up. The general conjecture remains open.
Known results and recent publication (date not stated)
- Complete bipartite graphs satisfy the conjectured bound.
- Connected -degenerate graphs satisfy it, with a stronger bound except for triangles.
- The order-one Levi graphs satisfy the stronger bound for and ; for , equality is claimed.
- Sahu and Padinhatteeri’s article, “Gallai’s Conjecture on Certain Families of Bipartite Graphs,” appeared in La Matematica; its accessible publication record gives no exact online date or theorem statement, while the associated preprint reports the result.
Community submission (unverified)
Posted September 9, 2026. A submitted argument studies the point–triple Levi graphs , claims exact path counts in some congruence classes of , and gives a ten-path decomposition for . It identifies the remaining cases with a uniform triple-terminal routing problem; none of these claims has independent verification.
Current status (as of September 2026): The conjecture is claimed for several graph classes, including , but remains open in general; the point–triple claims are unverified.
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Solutions 1
ProofGALLAI'S PATH DECOMPOSITION FOR POINT–TRIPLE LEVI GRAPHSSee full solution
We study Gallai's path-decomposition problem for the point–triple Levi graph Ln(m,3). Its bipartition consists
of the points of
and the 3-subsets of
, with incidence as adjacency. The graph has m + C(m,3) vertices
and 3C(m,3) edges. The parity of the point degree C(m-1,2) splits the problem modulo 4. When m is
congruent to 0 or 3 modulo 4, every vertex is odd and the classical odd-degree path-decomposition theorem
gives the exact value p(Ln(m,3)) =
/2. For m congruent to 1 or 2 modulo 4, the odd vertices are
precisely the triple vertices, yielding p(Ln(m,3)) at least C(m,3)/2. We verify equality explicitly for m=6 by a
ten-path decomposition. The remaining problem is formulated as a uniform triple-terminal routing problem.
Keywords: Gallai conjecture; path decomposition; path number; Levi graph; bipartite graph; incidence
graph; set systems; combinatorics.