  As the interest in adhesion is shifting towards smaller and smaller scales,
the well known Tabor adhesion parameter decreases and the DMT theory is
frequently considered to be the appropriate limit. A very attractive much
simplified version of DMT has been proposed in a recent investigation of rough
contacts by Pastewka & Robbins (PNAS, 111(9), 3298-3303, 2014) which seems to
work in very general conditions in numerical experiments. However, when
comparing this calculation to the known theories for the sphere, surprisingly
large conflicts occur, and the reason for the success of the numerical
experiments is obscure.
