how to use a surface split to remove all surfaces below the curve used to split the surface

Hi everyone, I am new to grasshopper and I have been working on a university project for an office tower and I have run into trouble when trying to trim part of my facade surface which is made of diamond panels. Being new to grasshopper I don't know the most effective way to do this so I have been trying to split the surface with a curve and remove the part of the surface below the curve, which hasn't seemed to work. 

I have attached my script and identified (bottom right corner of the script) the surface I am trying to 'split' or 'trim' and the curve i wish to split or trim the surface with. Any information on how i might best go about this would be great as i am somewhat on how to proceed. 

much appreciated.