help understanding formal grammar for subtraction example I am going through the following document trying to understand a simple grammar for a basic subtraction example (page 4).

The example states that


  Simple arithmetic expressions of arbitrary length built from the subtraction operator '-' and the numerals 0 and 1 can be described by the following grammar:

E = T "-" E | T
T = "0" | "1"



I understand T is the terminal symbols, but I am having a hard time understanding E.  What confuses me even more is when it is stated:


  Choosing the other alternative for E we might get the derivation...

E ==&gt; "0" "-" E



How and why is an alternative to E include E?  Likewise, I am having a hard time understanding how ET derives "0" or how EET derives 1.

Could someone better explain this to me?  I would greatly appreciate it to move forward in the document.  Maybe with a few examples would be extremely helpful.
T = "0" | "1" means that if you want a T string, 0 or 1 will
do.

E = T "-" E | T means that if you want an E string, a T string
followed by - followed by an E string will do, or a lone T
string will do.

Thus, for example, 1 is a T string, and is thus also an E
string. Hence, 1-1 is an E string since it follows the T "-" E
pattern.

Note that the double quote is just a notational device to distinguish
terminal symbols from non-terminal ones.

Can you go on from here?