Do we plan on using this anywhere else? If so, we should pull this out into its own file and put it in a `util` package or something.

If this is only used here for the `<IncrementalSolver,Solution>` pair, we should probably make it private, and use names that better reflect its meaning/use. Maybe something like `SolverSolutionPair`. At the very least, I think the internal variables should be `first` and `second` instead of `v` and `w`.