database( {
	mother( Child:string, Mother:string ),
      	father( Child:string, Father:string ),
	orphan( Person:string ),
	french( Person:string )
} ).

export parent( Child, Parent ).
export parent( $ChildX, Parent ).
export parent( Child, $Parent ).
export parent( $Child, $Parent ).

export ancestor( Descendant, Ancestor ).
export ancestor( $Descendant, Ancestor ).
export ancestor( Descendant, $Ancestor ).
export ancestor( $Descendant, $Ancestor ).

export ancestor1( Descendant, Ancestor ).
export ancestor1( $Descendant, Ancestor ).
export ancestor1( Descendant, $Ancestor ).
export ancestor1( $Descendant, $Ancestor ).

export ancestor2( Descendant, Ancestor ).
export ancestor2( $Descendant, Ancestor ).
export ancestor2( Descendant, $Ancestor ).
export ancestor2( $Descendant, $Ancestor ).

export ancestor3( Descendant, Ancestor ).
export ancestor3( $Descendant, Ancestor ).
export ancestor3( Descendant, $Ancestor ).
export ancestor3( $Descendant, $Ancestor ).

export same_generation( X, Y ).
export same_generation( $X, Y ).
export same_generation( X, $Y ).
export same_generation( $X, $Y ).

export same_generation1( X, Y ).
export same_generation1( $X, Y ).
export same_generation1( X, $Y ).
export same_generation1( $X, $Y ).

export same_generation2( X, Y ).
export same_generation2( $X, Y ).
export same_generation2( X, $Y ).
export same_generation2( $X, $Y ).

export same_generation3( X, Y ).
export same_generation3( $X, Y ).
export same_generation3( X, $Y ).
export same_generation3( $X, $Y ).

export bbf( X ).
export bbf( $X ).
export bbf0( X ).
export bbf0( $X ).

export relative( X, Y ).
export relative( $X, Y ).
export relative( X, $Y ).
export relative( $X, $Y ).

export individual( X ).
export individual( $X ).

%
% relative( X, Y )
%

relative( X, Y ) <- direct_relative( X, Y ).
relative( X, Y ) <- direct_relative( X, Z ), relative( Z, Y ), X ~= Y.

direct_relative( X, Y ) <- ancestor( X, Y ).
direct_relative( X, Y ) <- ancestor( Y, X ).

individual( X ) <- father( X, _ ).
individual( X ) <- father( _, X ).
individual( X ) <- mother( X, _ ).
individual( X ) <- mother( _, X ).
individual( X ) <- orphan( X ).
individual( X ) <- french( X ).

%
% parent( Child, Parent )
%       Parent is either the mother or the father of Child.
%

parent( Child, Father ) <-
	father( Child, Father ).
parent( Child, Mother ) <-
	mother( Child, Mother ).


%
% ancestor( Descendant, Ancestor )
%       Descendant is the descendant ( child, grandchild, etc. ) of Ancestor.
%
%

ancestor( Descendant, Ancestor ) <-
	parent( Descendant, Ancestor ).
ancestor( Descendant, Ancestor ) <-
	parent( Descendant, Parent ),
	ancestor( Parent, Ancestor ).

ancestor1( Descendant, Ancestor ) <-
	parent( Descendant, Ancestor ).
ancestor1( Descendant, Parent ) <-
	ancestor1( Descendant, Ancestor ),
	parent( Ancestor, Parent ).

ancestor2( Descendant, Ancestor ) <-
	parent( Descendant, Ancestor ).
ancestor2( Descendant, Ancestor ) <-
	ancestor2( Descendant, Ancestor0 ),
	ancestor2( Ancestor0, Ancestor ).

ancestor3( Descendant, Ancestor ) <-
	parent( Descendant, Ancestor ).
ancestor3( Descendant, Ancestor ) <-
	ancestor3( Ancestor0, Ancestor ),
	ancestor3( Descendant, Ancestor0 ).
	
%
% same_generation( X, Y )
%	X and Y are members of the same generation.
%

same_generation( X, Y ) <-
	parent( X, XParent ),
	same_generation( XParent, YParent ),
 	parent( Y, YParent ).
same_generation( X, X ) <-
	orphan( X ).

same_generation1( X, Y ) <-
	same_generation1( XParent, YParent ),
	parent( X, XParent ),
 	parent( Y, YParent ).
same_generation1( X, X ) <-
	orphan( X ).

same_generation2( X, Y ) <-
	parent( X, XParent ),
 	parent( Y, YParent ),
	same_generation2( XParent, YParent ).
same_generation2( X, X ) <-
	orphan( X ).

same_generation3( X, Y ) <-
 	parent( Y, YParent ),
	same_generation3( XParent, YParent ),
	parent( X, XParent ).
same_generation3( X, X ) <-
	orphan( X ).
	
%
% bbf( X )
%	X is a blue-blooded-frenchman.
%

bbf( X ) <-
	french( X ),
	orphan( X ).
bbf( X ) <-
	bbf( Mother ),
	mother( X, Mother ),
	bbf( Father ),
	father( X, Father ).

bbf0( X ) <-
	french( X ),
	orphan( X ).
bbf0( X ) <-
	mother( X, Mother ),
	bbf0( Mother ),
	father( X, Father ),
	bbf0( Father ).