First, observe that (1) actually contains an equivalent statement of the hypothesis:
So any work should follow these.
Incidentally, if we add these and then divide by 2, we get (1).
This got me confused as I have not used proportionality for a very long time, all functions I deal with now are non-affine.
If a is proportional to b and a is prortional to d, which of the following is correct:
(1) and so