Mass addition into expression node

How to write the function to replicate the “mass addition” behavior into the expression node?
this form does not work.

Cattura|690x229

furthermore, sometimes I find hard reading the expression function notation, can somebody help me understanding the meaning of this? Σ(x[.y.z._])??

Use the Mass Addition component and add an input for it to the Expression or Evaluate components.

Thanks for the fast replay, this solution works for this simple case indeed, however I wanted to use the expression node to compact the algorithm, and the mass addition is an intermediate step of the formulation so I would like to avoid using it 100% otherwhise there would be no point at all to use the expression node in the first place.

Expression component doesn’t support that.

Really?! so what the summation simbol stands for?