Relation algebra
In mathematics and abstract algebra, a relation algebra is a residuated Boolean algebra expanded with an involution called converse, a unary operation. The motivating example of a relation algebra is the algebra 2 X 2 {\displaystyle 2^{X^{2}}} of all binary relations on a set X {\displaystyle X} , that is, subsets of the cartesian square X 2 {\displaystyle X^{2}} , with R ∙ S {\displaystyle R\bullet S} interpreted as the usual composition of binary relations R {\displaystyle R} and S {\displaystyle S} , and with the converse of R {\displaystyle R} as the converse relation.