/*
 
                     +----------------+
                     | IPhList        |
                     +----------------+
                             |
                            / \
                            ---
                             |
                -----------------------------
                |                           |
        +---------------+           +----------------+
        | MtPhList      |           | ConsPhList     |
        +---------------+           +----------------+
                                 +--| PhEntry first  |
                                 |  | IPhList  rest  |
                                 |  +----------------+
                                 |
                                 V
                        +----------------+
                        | PhEntry        |
                        +----------------+
                        | String  name   |
                        | int     num    |
                        +----------------+
                        
                        
*/

// to represent a list of phone entries
public interface IPhList { 
}