= Solution
A <gauge anomaly> breaks a redundancy needed to remove unphysical states and makes a quantum gauge theory inconsistent unless it cancels. A <chiral anomaly> is instead the quantum violation of a classical global axial current; the theory remains consistent, but processes such as $\pi^0\to\gamma\gamma$ and instanton-induced charge violation become possible. A <'t Hooft anomaly> is an obstruction to gauging a global symmetry. It is compatible with a consistent theory but is invariant under renormalization-group flow, so any infrared phase must reproduce it through massless fields, spontaneous symmetry breaking, or topological degrees of freedom.
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