reserve Y,Z for non empty set;
reserve PA,PB for a_partition of Y;
reserve A,B for Subset of Y;
reserve i,j,k for Nat;
reserve x,y,z,x1,x2,y1,z0,X,V,a,b,d,t,SFX,SFY for set;

theorem
  %I(Y) '<' %O(Y)
proof
  ERl(%O(Y)) = nabla Y by Th33
    .= [:Y,Y:];
  then ERl(%I(Y)) c= ERl(%O(Y));
  hence thesis by Th20;
end;
