Instead of naming these operations, we could use '+' and '-', with semantics:

# Set the values of the variables.

>>> a = 'hello '

>>> b = 'world'

>>> c = 'hello world'

# Some values between the variables.

>>> a + b == c

True

>>> a == c - b

True

>>> b = -a + c

True

# Just like numbers except.

>>> a + b == b + a

False

This approach has both attractions and problems. And also decisions. The main issue, I think come to this. Suppose we have

a, A = ('a', -'a')

b, B = ('b', -'b')

a + A == A + a == ''

b + B == B + b == ''

A + '' == '' + A == A

B + '' == '' + B == B

together with unrestricted addition of a, A, b, B then we have what mathematicians call the free group on 2 letters, which is an enormous object. If you want the math, look at, https://en.wikipedia.org/wiki/Free_group#Examples

We've made a big mistake, I think, if we allow Python programmers to accidentally encounter this free group. One way to look at this, is that we want to cut the free group down to a useful size. One way is

>>> 'hello ' - 'world' == 'hello' # I like to call this truncation.

True

Another way is

>>> 'hello' - 'world' # I like to call this subtraction.

ValueError: string s1 does not end with s2, so can't be subtracted

I hope this little discussion helps with naming things. I think this is enough for now.

Jonathan