  Note the last line. Here again, Frege uses the identity sign to help state the material equivalence of two concepts. He can do this because materially equivalent concepts \(F\) and \(G\) are such that \(F\) maps an object \(x\) to The True whenever \(G\) maps \(x\) to The True; i.e., for all arguments \(x\), \(F\) and \(G\) map \(x\) to the same truth-value.