+ # `b` is not a single char, so just use except
+ # "a - b == a Except (Any* b Any*)"
+ var any1 = new Automaton.cla(0, null)
+ any1.close
+ var any2 = new Automaton.cla(0, null)
+ any2.close
+ var b2 = any1
+ b2.concat(b)
+ b2.concat(any2)
+ var c = a.except(b2)
+ return c