database( { word( string ) } ).

%
% Import predicate to split words from C++
%
import foreign all_letters( $Word: string, Letter: string,
			    Position: integer)
	from '/home/natraj/new_ldl++/system/demo/all_letters.o'.

export common( Word1, Word2 ).
export all_letters( $Word, Letter, Position ).

%
% Collect all letters of a word into a set
%
group_letters( Atom, < Letter > ) <-
    all_letters( Atom, Letter, _ ).

%
% Find words that are closely related. That is,
% over half of the letters that appear in either
% word also appear on the other word.
%
common( Word1, Word2 ) <-
    word( Word1 ),
    word( Word2 ),
    group_letters( Word1, Set1 ),
    group_letters( Word2, Set2 ),
    intersection( Set1, Set2, Inter ),
    union( Set1, Set2, Union ),
    cardinality( Union, UCard ),
    cardinality( Inter, ICard ),
    ICard > 0.5*UCard.