Consider a binary operation # that is closed under the set of integers (if a and b are integers, then a#b is an integer).
Assume that, for all integers a and b, it is true that (a#b)#a=b.
Prove that a#(b#a)=b.
(In reply to
re(2): A simple solution by Charlie)
Yes, you are correct. I misspoke. And that, too, cannot be assumed about the problem.
Thanks, Charlie.