- #1
Syrus
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Homework Statement
*Attached is the problem statement, along with a definition which is to be used (I feel like some of the definitions in this text are somewhat untraditional, so I am including this one for clarity).
Edit* sorry, it's problem #31.
Homework Equations
The Attempt at a Solution
Let <T, !> be any binary structure isomorphic with <S,*>. This means there is some bijection Ψ: S → T such that (∀s1,s2 ∈ S)(Ψ(s1*s2) = Ψ(s1)!Ψ(s2)). Now let d ∈ T. Since Ψ is surjective, there is some c ∈ S such that Ψ(c) = d. But then there is some x ∈ S such that x*x = c. As a result, Ψ(x*x) = Ψ(c) = d = Ψ(x)!Ψ(x).
Q.E.D.