There are many proofs. Then use 8.15 enough times to get univ. Assume left side. Use the standard method to get each universal as a temp. R are temp.
R is a temp.
There are undoubtedly many other correct proofs, and the students found even more incorrect ones. One of the two wffs B , C below is a theorem with a very short and simple proof, and the other is not even a valid formula. Do nothing with the other wff. Again, there are MANY proofs. Then 9.12 is staring one in the face.