Chris Angelico asked: what does a negative string look like?

This is a very good question. It looks a bit like a negative number.

>>> 2 + 2

>>> len('aa' + 'bb')

>>> len(-'bb')

-2 # Odd, I must confess.

>>> 5 + (-1)

>>> len('hello')

>>> len(-'o')

-1

>>> 'hello' + (-'o')

'hell'

>>> len('hello' + (-'o'))

Grade school: How can I possible have -3 apples in my bag.

University: How can I possibly be overdrawn in my bank account.

Negative strings are similar to negative numbers except:

For numbers a + b == b + a

For strings a + b != b + a

It is the non-commuting that make negative strings difficult. This is a bit like computer programming. It's not enough to have the correct lines of code (or notes). They also have to be put in the right order.

I hope this helps. I do this sort of math all the time, and enjoy it. Your experience may be different.

Jonathan