  Boundary theories of static bulk topological phases of matter are obstructed
in the sense that they cannot be realized on their own as isolated systems. The
obstruction can be quantified/characterized by quantum anomalies, in particular
when there is a global symmetry. Similarly, topological Floquet evolutions can
realize obstructed unitary operators at their boundaries. In this paper, we
discuss the characterization of such obstructions by using quantum anomalies.
As a particular example, we discuss time-reversal symmetric boundary unitary
operators in one and two spatial dimensions, where the anomaly emerges as we
gauge the so-called Kubo-Martin-Schwinger (KMS) symmetry. We also discuss mixed
anomalies between particle number conserving U(1) symmetry and discrete
symmetries, such as C and CP, for unitary operators in odd spatial dimensions
that can be realized at the boundaries of topological Floquet systems in even
spatial dimensions.
