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Looking at your current code, why did you move it outside of the function? If you move it back inside, your code might work.

guys whats the answer

Tests do not necessarily test for "-1" being the coefficient of the term with the highest power of the variable (e.g. the x^3 coefficient of (-x+1)^3 is -1). In this case, my original code would have returned -1x^3 + ..., yet it passed because this case was not tested (I ran it again because I removed some print() statements, and then it failed).
Brilliant kata, though—thanks!

Rust sample tests expect the function to be named expand_binomial, but the initial code and the full set of tests expect expand.

yay i hate math

Since Python 3.9, typing aliases like Tuple, List, or Set are deprecated because the type themselves (tuple, list, set ...) now directly support the [] operator. The type hints in the initial code should be rewritten in consequence

added + upgraded to chai assertions for JS + using approximate equality, considering the result is a float

i added this:

public override int GetHashCode()
{
  return (X, Y).GetHashCode();
}

I love this kata, I really liked that it can be solved step by step

Fun kata!

Approved

Very good and funny Kata! Thanks to author!!!

i got confused and thought that 0x+b was possible

apparently not

how is that one only 4kyu

Prolog translation