The enum() function maps a predecessor element x(t1) with age t1 to produce two successor elements x1(t1+1) and x2(t1+1) with age t1+1.
The elim() function eliminates all elements whose age t is greater than 2.
As an example, suppose P0={ john(2), mary(1)}.
P1= enum(P0)={ john1(3), john2(3), mary1(2), mary2(2)}.
P2 = elim(P1)={mary1(2), mary2(2) }.
The visual expression is: (cycle1: [guard1,1] P0 -enum< P1 >elim- P2). The functions enum() and elim() can be represented by icons. The deployment of this visual expression is the visualization of the sequence of sets P0, P1 and P2. We can specify the visual expresion in XML, and build a transformer to transfom the visual expression into XML statements for the visualization of P0, P1 and P2.