Wertverlauf and the problem of expansion

pp. 58-81

in: Christian Thiel, Sense and reference in Frege's logic, Berlin, Springer, 1968

Abstract

According to the view usual in logic, two concepts are to be attributed the same extension if and only if every object which falls under one concept also falls under the other. If one takes the concepts as special functions (as above), then two concepts will have exactly the same extension if they take the same value for every argument. This can be very simply generalized.