learning from models

I was wondering, is there away to undo a smooth/subsurf modifier if they already applied it and deleted the history? I tired decimate but that didnt do anything

You can start from an outside edge or from a pole and delete every second edgeloop, or add a decimate modifier and choose the unsubdivide option and a level of two. But neither method will really get back to the original shape. It will be smaller and smoother than it was to begin with. The decimate modifier will leave some of the mesh triangulated. and if you’re deleting edgeloops, if you don’t select and delete them all at once the edgeloop select will get loose into geometry you want to keep.

thank you. could I keep applying the decimate modifier and dissolving edge loops? or does decimate really work once?