A generalisation is confirmed by any of its instances. If two hypotheses can be known a priori to be equivalent, then any data that confirm one confirm the other. The paradox runs as follows.
All ravens are black.
Everything nonblack is a nonraven. This nonblack thing is a nonraven. By G1, P1 confirms R2, and hence, by E1, confirms R1 too. I agree with Sainsbury that rejecting E1 is not a viable option. The issue turns on the presuppositions involved in assertions of R1 and R2 on particular occasions of use.