I'm sorry if this seems like a question asked before doing any research, but the discrete math textbook I'm using doesn't mention it, and I tried googling it, but I don't even know the name of it, so I couldn't find anything either.
The original question is: Let A be a set and R $\subseteq A \times A$ be a binary relation on A. Prove that R is reflexive $\Leftarrow\Rightarrow R^0\subseteq R$
I would just like to know what $R^0$ means here.