1. The problem statement, all variables and given/known data Suppose f and g are isomorphisms from U to V. Prove of disprove each of the following statements: a) The mapping f + g is an isomorphism from U to V. 2. Relevant equations 3. The attempt at a solution I have no idea where to start.. do I need to show that f and g are 1-1 and onto? Or do I go from something like f(u) + g(u) = (f+g)(u)? Isn't that defined by a property of composition of function..?