  According to the Integrated Information Theory of Consciousness,
consciousness is a fundamental observer-independent property of physical
systems, and the measure Phi of integrated information is identical to the
quantity or level of consciousness. For this to be plausible, there should be
no alternative formulae for Phi consistent with the axioms of IIT, and there
should not be cases of Phi being ill-defined. This article presents three ways
in which Phi, in its current formulation, fails to meet these standards, and
discusses how this problem might be addressed.
