Thank you Dipo for the quick response.

But, that is not really what I am looking for.

Let's assume "a" = 10, then "b" should be {2:5:1}. Now, if "b" = 5 then "d" = 5 (only); on the other hand, if "b" = 2 then "d" can be anything between 2 (i.e. "b") and 8 (i.e. "a-b")

So, basically, for random value of "a" from:** a = {10:20:2} **

**b = {2:0.5*a:1}**

**d = {b:a-b:1}**

I know that above doesn't work!

The question is: How to setup this? The figure in the original post may help to clarify the situation.