  Amorphous systems of soft particles above jamming have more contacts than are
needed to achieve mechanical equilibrium. The force network of a granular
system with a fixed contact network is thus underdetermined, and can be
characterized as a random instantiation within the space of the force network
ensemble. In this work, we show that by examining the boundaries of this space
of allowed force networks, defect contacts which are not necessary for
stability of the system can be uniquely identified. We further show that in the
near jamming limit, this identification is nearly always correct and the defect
contacts are broken under decompression of the system.
