The node will have one child. It owns it.
|  NodeUn (UnOper* op, Node* node, unsigned line)
 | NodeUn | 
Caller must not delete / modify pointers.
Parameters:
| op | unary operation associated with node. | 
| node | child of node -- argument of operation. | 
| line | line of configuration where node was created. | 
|  ~NodeUn ()
 | ~NodeUn | 
|  DEFINE_VISITABLE ()
 | DEFINE_VISITABLE | 
| const UnOper&  op ()
 | op | 
[const]
Returns: unary operation associated with node.
| Node&  node ()
 | node | 
[const]
Returns: argument of unary operation.