 Alonzo Church used Carnap’s concept of intensional isomorphism in his reconstruction of Frege’s notions of sense and reference, “A formulation of the logic of sense and denotation” (Church 1951), and later also addressed a critique to Carnap directly (Church 1954), to which Carnap (1954b) replied. John Myhill (1958) in a critique of Church’s reconstruction, re-discovered a paradox first spelled out by Russell in Appendix B of Principles that raises precisely the same issue about individuating intensions, and since then the study of Russellian intensional logic, and finer-grained versions of intensional identity, has continued (Church 1976, 1985; Linsky 1988; Anderson 1989; Cantini 2004; Deutsch 2014).