Some new theorems

I added the following theorems to Funcoids and Reloids article. The theorems are simple to prove but are surprising, as do something similar to inverting a binary relation which is generally neither monovalued nor injective.

Proposition Let , , are binary relations. Then .

Theorem Let , , are sets, , , . Then

Theorem Let , , are sets, , , . Then

The above theorems are the key for describing product funcoids, a task I previously got stuck. Now I can continue my research.