  While it has become widely appreciated that (higher) gauge theories need,
besides their variational phase space data, to be equipped with "flux
quantization laws" in generalized differential cohomology, there used to be no
general prescription for how to define and construct the resulting
flux-quantized phase space stacks.
  In this short note we observe that all higher Maxwell-type equations have
solution spaces given by flux densities on a Cauchy surface subject to a higher
Gauss law and no further constraint: The metric duality-constraint is all
absorbed into the evolution equation away from the Cauchy surface.
  Moreover, we observe that the higher Gauss law characterizes the Cauchy data
as flat differential forms valued in a characteristic L-infinity-algebra. Using
the recent construction of the non-abelian Chern-Dold character map, this
implies that compatible flux quantization laws on phase space have classifying
spaces whose rational Whitehead L-infinity algebra is this characteristic one.
The flux-quantized higher phase space stack of the theory is then simply the
corresponding (generally non-abelian) differential cohomology moduli stack on
the Cauchy surface.
  We show how this systematic prescription subsumes existing proposals for
flux-quantized phase spaces of vacuum Maxwell theory and of the chiral boson.
Moreover, for the case of NS/RR-fields in type II supergravity, the traditional
"Hypothesis K" of flux quantization in topological K-theory is naturally
implied, without the need, on phase space, for the notorious further duality
constraint. Finally, as a genuinely non-abelian example, we consider
flux-quantization of the C-field in 11d supergravity/M-theory given by unstable
differential 4-Cohomotopy ("Hypothesis H") and emphasize again that,
implemented on Cauchy data, this qualifies as the full phase space without the
need for a further duality constraint.
