Two binary relationships need an intermediate element as a bridge to synthesize a binary relationship. This is the definition of relationship synthesis.

If we can list all the contents contained in the two relationships, then we can compare them one by one when solving them. For example:

If: r = {

Then: r ○ s = {

If a set is defined in a descriptive way (a relationship is also a set), then we can't list all the elements and can only use symbols (variables), such as this problem. Here is a variable that describes this relationship.

Known: r = {

Then: the inverse of r (let's set it as a) = {

For the first question, according to the comprehensive definition, the elements in B○R

This means that Z is the mother of X and Z is the father of Y. ..

That's the reason for Z, but the analysis you said seems to have reversed the two topics.