case 0: return Empty.INSTANCE; case 1: return s.simplified.get(0); default: return new Concatenation(s.simplified);
case 0: return Empty.INSTANCE; case 1: return s.simplified.get(0); default: return new Concatenation(s.simplified);
case 0: return Empty.INSTANCE; case 1: return s.simplified.get(0); default: return new Concatenation(s.simplified);
case 0: return Empty.INSTANCE; case 1: return s.simplified.get(0); default: return new Concatenation(s.simplified);