Resolve non-QUBO constraints

[Damian Rovara]

Currently, some cost functions are not QUBO. Employ one of these solutions:

• Reduce the order by introducing additional variables in the final step
• Pick variables in a smart fashion
  • re-use existing ones
  • re-order variables for maximum re-use
    • greedy
    • good algorithm (NP-hard?)
  • simplify some cases (e.g.: given $y = x_1x2$, reduce $yx_2$ to $y$)