lSuppose the input string is Òa b + cÓ.
lThe parser calls S1(Òa b + cÓ).
lS1 calls V1(Òa b + cÓ).
lV1 identifies a, returns success and unparsed input Òb + cÓ.
lS1 checks for + and does not find it; therefore S1 returns
success, with Òb + cÓ.
lSince the top-level call to S1 has returned, but there is residual
input, the string is not
accepted.