Multiple Load cases Expression Builder

Hi all, 

It may sound very simple but i'd like to create an expression in the 'Expression Builder' of HyperView using results of two different loadcase.

For example i want to Substract the Stress tensor P3(minor) component from my loadCase A to the Stress tensor P1(minor) component from my loadCase B.

I can't find any solution, 

Thank you for your help