1. Aug 18, 2009

### Petar Mali

$$A=\pm\sum_j\frac{1}{p_{ij}}$$

So I can always say

$$A+X=-(A-X)$$ or $$-A=A$$

Can I sometimes problem with this?

2. Aug 21, 2009

### olgranpappy

There seems to be a problem... unless you want A=0.