Frege on identity sentences

Interpretations from the past 30 years of frege's explanation of the cognitive value of identity sentences are considered. Frege's explanation, Which the author finds superior to any of these interpretations, Is that 'a=b' has greater cognitive value than 'a=a' because, Given that 'a' and 'b' are different sign-Types, The sense of 'a' "may" (though it need not) differ from that of 'b'. It is pointed out that this interpretation of frege shows that his problem with identity sentences can be resolved prior to the larger problem of explicating the notion of sense