A state in the NFA corresponding to a regular expression.
Each regular expression literal
l has one accepting state
Accept(l), one state that accepts all suffixes
and a state
Match(t, i) for every subterm
which represents the state of the NFA before starting to
t, or the
ith character in
t is a constant.
Gets the term represented by this state.
Gets a string representation for this state in a regular expression.