/* Family Tree */

parent(pete,ian).     % Pete is a parent of Ian
parent(ian,peter).
parent(ian,lucy).
parent(lou,pete).
parent(lou,pauline).
parent(cathy,ian).

female(cathy).        % Cathy is female.
female(lucy).
female(pauline).
female(lou).

male(ian).            % Ian is male.
male(pete).
male(peter).


/* X is the mother of Y if X is the parent
   of Y and X is female                   */

mother(X,Y):- parent(X,Y),female(X).