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/* Answers to worksheet 3 */
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/* NOTE THE ORDER OF CLAUSES AND SUBGOALS IN THE RECURSIVE DEFINITIONS */

/* Exercise 3.1: Family trees                                       */
/* For these definitions to work you have to load in facts such     */
/* as those given in the file family.                               */


/* a) Nonrecursive definitions of grandparent and great-grandparent */

grandparent(Gradparent, Grandchild) :- parent(Grandparent, Parent),
                                       parent(Parent, Grandchild).

great_grandparent(GGrandparent, GGrandchild) :- 
                                  parent(GGrandparent, Grandparent),
                                  grandparent(Grandparent, GGrandchild).

/* b) Recursive definition of ancestor                              */

ancestor(A, D) :- parent(A, D).
ancestor(A, D) :- parent(A, Int), ancestor(Int, D).


/* Exercise 3.2: Evolution                                          */
/* For these definitions to work you have to load in facts such     */
/* as those given in the file evolution.                            */
 

higher(C1, C2) :- evolved(C1, C2).
higher(C1, C3) :- evolved(C1, C2), higher(C2, C3).


/* WITH THE CLAUSES AND SUBGOALS ORDERED IN THE WAY SHOWN HERE,     */
/* ALL DEFINITIONS WILL BE POLYMODAL.                               */