Small-trade conjecture for subsets of Latin squares

Let LL be a Latin square of order n3n\geq 3, and let SS be a subset of its entries with Sn2/4|S|\leq \left\lfloor n^2/4\right\rfloor. For a Latin trade TT in LL, let R(T)R(T), C(T)C(T), and E(T)E(T) denote respectively the numbers of rows, columns, and elements involved in TT. Small-trade conjecture. There exists a Latin trade TLT\subseteq L such that

TS=T\cap S=\varnothing

and at least one of R(T)3R(T)\leq 3, C(T)3C(T)\leq 3, or E(T)3E(T)\leq 3 holds. This conjecture is motivated by the use of small trades to rule out small uniquely completable or critical sets. It is stated as a conjecture in the paper; no resolution beyond the discussion and the verified order-seven case is supplied here.

Sources & referencesView supporting material

Primary source

Richard Bean, “The size of the smallest uniquely completable set in order 8 Latin squares”, arXiv:math/0403005 (2004).

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