When I use proportional editing, I want some vertices to be fixed at where they are.
If you know how to fix the global coordinates of vertices, can you please tell me?
In the normal course of editing, you can H hide elements you don't want to affect.
But then, you can't see them... So, if you want to, you can AltD make an instance of the object, left in Object Mode, so you can see what you're doing: