@mattbrendzel, @nbeck the problem lies with the parentheses on the class name Sudoku() and passing self as parameter to the method. Try removing these. Also, write an initialize method.

Hey Giacomo, a few questions:

1. why use item[0].length>0 instead of !item[0].empty?
2. why use "and" and "or", instead of && and || on the same line?
3. why "0123456789".index(item[0][item[0].length-1])!=nil instead of item[0][item[0].length-1] =~ /\d/ != nil
4. Why is it necessary to say (res[item[1]] or 0)?

Good kata, just a few spelling and grammatical issues. The title should be "Simplifying multilinear polynomials".
There are also a few grammatical issues in the description that I can point out, if you'd like.

Thanks, I'll do that

Thanks, I'll do that

@GiacomoSorbi haven't really contributed to this site before, but is there any way to suggest spelling and grammatical improvements to the author? There are a few errors, including in the title

From the description, your function should be case insensitive to the vowels.

What is $1?

What is $1?

Use chars instead of split(//). It's several times faster and (IMO) more readable

The string contains some whitespace alongside the apostrophe. Try return [] if text.gsub(/\s/, '') == "'" (credit @frunns)

Why is ||= necessary in creating the hash? Is that an or assignment operator?

any reason you used the or keyword instead of ||?

why did you move letters out of the method and make it global?