 As is standard in proof theory, the way to read these rules of inference is that above the horizontal rule \(\frac{}{\phantom{X=X}}\) are the  premises of the rule (which are equations) and the equation below the horizontal rule is the conclusion of the rule of inference. In the case of the reflexivity rule, nothing is written above the horizontal rule. We understand such a case as saying that, for all terms \(X\), we may infer the equation \(X = X\) from no premises.