@Override
	public String toString() {
		return _rules.stream()
			.map(Objects::toString)
			.collect(Collectors.joining("; "));
	}
Maps {@code this} TRS from type {@code V} to type {@code B}.

@param mapper the type mapper
@param <B> the target type
@return a new TRS for the mapped type
@throws NullPointerException if the {@code mapper} is {@code null}
jenetics.ext/src/main/java/io/jenetics/ext/rewriting/TRS.java