Solution
= Solution
A <gauge anomaly> makes gauge redundancy inconsistent and must cancel. A <chiral anomaly> is the quantum nonconservation of a classically conserved axial current and may be a physical effect. A <'t Hooft anomaly> is an obstruction to gauging a global symmetry; it is preserved by <renormalization-group flow> and must be reproduced by the infrared theory, through massless degrees of freedom, symmetry breaking, or topological order.