 Rule R: From \(\bC\) and \(\bA_{\alpha} = \bB_{\alpha}\), to infer the result of replacing one occurrence of \(\bA_{\alpha}\) in \(\bC\) by an occurrence of \(\bB_{\alpha}\), provided that the occurrence of \(\bA_{\alpha}\) in \(\bC\) is not (an occurrence of a variable) immediately preceded by λ.