This is a well-formed parentheses string checker.
Adopted from Prather, page 481. (Note that the left parenthesis
has three contexts in this file.)
(0((0R
(0)A1L
(0AA0R
(0 2L
(1(A0R
(1AA1L
(1 NR Prather has 0 instead of R
(2((NR Prather has 0 instead of R
(2AA2L
(N--NR Never used. Its existence forces N to be a non-final state.
(2 YR