We defined the class $\text{DP}$ like this:
$$\text{DP} := \{ A \setminus B : A, B \in \text{NP} \}$$
We say a problem $P$ is $\text{DP}$ complete iff $P \in \text{DP}$ and $X \leq P \forall X \in \text{DP}$, meaning that every language $X \in \text{DP}$ can be reduced to $P$ in polynomial time.
For a particular problem (which I do not expect you to solve, so I won't explain all the details), I already proved that $P \in \text{DP}$, but I do not know how to continue. Also, I could not find more information about this class.
Could someone give me a hint how to start such a proof or point me to further information about this complexity class which might help me to achieve it?
Edit: The definition is from a lecture about complexity of algorithms. The task is to prove that
$$\text{SAT-UNSAT} = \{\, (F,G) : F \text{ is satisfiable}, G \text{ is not}\, \}$$
is DP-complete. I proved that $\text{SAT-UNSAT} \in \text{DP}$, but I failed to prove the completeness.