block(b1).
block(b2).
block(b3).
block(b4).

on(b1,table,0).
on(b2,table,0).
on(b3,table,0).
on(b4,b3   ,0).

%                 b4
%                 b3
%        b4  -->  b2
%  b1 b2 b3       b1

:- not on(b1,table,#maxint).
:- not on(b2,b1   ,#maxint).
:- not on(b3,b2   ,#maxint).
:- not on(b4,b3   ,#maxint).
