Canonical rules for fraction numerators

Hi all! I’m super interested in MathJSON, and I’m trying to set up MathLive/Compute in a personal project.

I was working on comparing linear equations with simplify/evaluate/canonical and found that I couldn’t get a consistent representation for (-7/4)x+10

const answerbox="\\frac{-7x}{4}+10"

const answer = [  "Add", [ "Multiply", [ "Divide", -7, 4 ], "x" ], 10]

  match(
    ce.evaluate(ce.parse(answerbox)),
    ce.evaluate(answer)
  )
);

Is this a case where I need to use additional rewrite rules to coerce this into a unique ‘canonical’ form for comparison, or is this within the scope of the canonical function?

[stefnotch]

Here is the relevant sympy documentation. Typing the following into the sympy live shell (bottom right of the documentation page) does demonstrate that behavior:

expr = x/y
srepr(expr)

Of course if that turns out to be more trouble than it’s worth, that’s an entirely valid reason for not including it.

[arnog]

It feels a bit weird to me to not have division in the canonical form (admittedly, an earlier version of the Compute Engine did just that). That also makes some simplification rules more difficult to write since instead of detecting patterns of the form a/b you now have to pick up a*c*d where c (or d) is of the form b^-1.

Can you tell me more about Sympy’s expectations in that regard? Do you have a pointer in the documentation that discusses this and perhaps a rationale for it?

On a broader note, I intend in an upcoming revision, to have clearer lines between ‘formatting’ (i.e. putting into a canonical form) and ‘simplifying’. Formatting will not account for any calculations (i.e. multiply by 1), but will focus on sorting arguments of commutative functions, and reducing associative, idempotent and involutory functions. Simplify on the other hand will apply more rules, including ones depending on the numerical values of the arguments, and other ‘assumptions’ about arguments (for example whether an argument is a positive real, or a complex number, etc…