R and a and b are convertible w.r.t. Then R reduces b to a . Let a , b , c be sets. We introduce R has diamond property as a synonym of R is subcommutative. For all sets a , b such that a and b are divergent w.r.t.
R holds a and b are convergent w.r.t.
For all sets a , b such that a and b are convertible w.r.t. R holds a and b are convergent w.r.t. Let R be a binary relation. Suppose R is subcommutative. Let a , b , c be sets.