Ranks of Incidence Matrices of Steiner Triple Systems.
Ranks of permutative matrices
A new type of matrix, termed permutative, is defined and motivated herein. The focus is upon identifying circumstances under which square permutative matrices are rank deficient. Two distinct ways, along with variants upon them are given. These are a special kind of grouping of rows and a type of partition in which the blocks are again permutative. Other, results are given, along with some questions and conjectures.
Regular elements of the semigroup of all binary relations.
Relationships between conbinatorics and 0-simple semigroups.
Remark to a problem on 0-1 matrices