  Flux quantization of the C-field in 11d supergravity is arguably necessary
for the (UV-)completion of the theory, in that it determines the torsion
charges carried by small numbers of M-branes. However, hypotheses about C-field
flux-quantization ("models of the C-field") have previously been discussed only
in the bosonic sector of 11d supergravity and ignoring the supergravity
equations of motion. Here we highlight a duality-symmetric formulation of
on-shell 11d supergravity on superspace, observe that this naturally lends
itself to completion of the theory by flux quantization, and indeed that 11d
super-spacetimes are put on-shell by carrying quantizable duality-symmetric
super-C-field flux; the proof of which we present in detail.
