### Zero sums: the final cut

You have already done the heavy lifting in proving that `x + y = 0 => y = 0`

. If you would like to take this result to its logical
conclusion, you could try this *optional* bonus problem.

*Hints:* Remember that you can turn the `==`

into two conditionals.
Also it turns out that `(A => B) & (A => C) => (A => B & C)`

.

#### Where to go from here?

Some ideas: