### Question:
Require extends PrimitiveStackMapping { @Override public int arity() { return 2; } Require(); @Override int arity(); String[] getIdentifiers(); Parameter[] getParameters(); String getComment(); void apply(final RippleList arg,
                      final Sink<RippleList> solutions,
                      final ModelConnection mc);  }### Answer:
@Test public void testArity() throws Exception { assertReducesTo("2 2 1 add. (add. 5 equal.) require.", "2 3"); assertReducesTo("1 1 add. 3 (add. 5 equal.) require.", "1 1 add. 3"); }