Difference between two set of surfaces

Hi!

I need some help with this gh. I want to select the not equilateral triangles from one list. I have the equilateral triangles in other list and i tried to use "set difference" component to obtain the not equilateral triangles. And i always have the same message "Invalid cast surface" > primitive data type.  

Could someone knows another method or explain me what i do wrong with the set?

Thanks.