lThere is a Òstart symbolÓ, or ÒrootÓ, say S, which is not in the alphabet of the
language itself.
l¨
is a symbol meaning Òcan be rewritten asÓ.
lGrammar rules, for example:
1.S ¨ ab
2.S ¨ aSb
3.S ¨ SS
lApplication of rules is by Òfree choiceÓ.
lA sequence of applications is called a derivation.
lThe strings in the language are those that donÕt include S.