multiply fractions edge case to support cancelling

[evykassirer]

there are some cases where we don't want to multiply fractions with other things, one of them is 9/2 * x -> 9x / 2 (since this doesn't change anything and could be considered less readable)

a case we're not handling with the current logic, that should multiply is:

x * 6/x -> (x * 6) / x (which is needed for cancelling out)

one solution is just to have better cancelling code that doesn't only work with the fraction 6x/x, and can recognize that x cancels with the denominator in 6/x

another (possibly easier for now) solution would be to add a case for multiplying a symbol times a term with a symbol in the denominator

... this is a bit messy, so I'm not sure what the best solution is - open to suggestions!

this came up because of a case in #88

[kevinbarabash]

my vote would be for better canceling code.

[aelnaiem]

I agree with @kevinbarabash, let's improve the canceling code so it handles this case

[evykassirer]

I'd love for that to happen :) just haven't had the time to figure out the best way for that to work

[ldworkin]

Fixed by 344d15b