  The full 6d Hopf-Wess-Zumino term in the action functional for the M5-brane
is anomalous as traditionally defined. What has been missing is a condition
implying the higher analogue of level quantization familiar from the 2d
Wess-Zumino term. We prove that the anomaly cancellation condition is implied
by the hypothesis that the C-field is charge-quantized in twisted Cohomotopy
theory. The proof follows by a twisted/parametrized generalization of the Hopf
invariant, after identifying the full 6d Hopf-Wess-Zumino term with a twisted
homotopy Whitehead integral formula, which we establish.
