That is true, but that would be the definition of +. The OP is referring to the application of that operator to its arguments, which (depending on semantics) could also be a set of sets, or it could be a rewriting (ie, time based) process.
Anything you can do as a sequence of operations on symbols can be written out, and then there you have it, on the page, all at once!
Time does not appear in formal logic or number theory, even though it is convenient to think of a derivation or a calculation as as sequence of steps performed one at a time.
it is also very convenient to use mathematics to model a temporal process, but we can, and often do, then show what happened (or will happen) as tables, graphs or other static representations.
I know that last sentence presupposes time, but I am not even going to attempt to rewrite it in a way that avoids doing so!
