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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
I agree, you can't assume people using this site have taken a Calculus course.
Suggestion
It's never been the case that the instructions for Codewars Kata should include common formulas.
Just so you know, I didn't write the Java version.
I agree. I think the author doesn't know that a null string is not the same as an empty string. In Java, we have:
String aNullString = null;
String anEmptyString = "";
aNullString.equals(anEmptyString) returns false.