Symbol s = a letter or a word
Notation a or
w
Possibly followed by ? or
*. Notation: a?, a*, w?, w*
Factor f = s | s | . . . | s
Notation: s
or +s (e.g. (+w*) or (+a*)? or (w*)? )
Possibly followed by ? or
*
Simple RE = f.f
.f
Notation: RE(f1, f2,
, fk) where f1,
, fk are the kinds of factors allowed