I'm currently working with some pseudodifferential operators of Hormander class $L^{m}_{\frac{1}{2},\frac{1}{2}}$ and unfortunately many of the usual tools break down, due to difficulties with their asymptotic expansion. In particular, I know a version of Egorov's theorem holds for such operators, but the reference I know for that result (Taylor's Pseudodifferential Operators) is out of print and difficult to find. He doesn't cover this case in the second volume of Partial Differential Equations, either.
Hormander briefly mentions this class in volume three of The Analysis of Linear Partial Differential Operators, but doesn't provide much guidance on how to modify Egorov's theorem.
Is there a better reference for this fact, and for this exotic symbol class in general? I feel a bit bad about referring to Taylor's book when I know copies of it are few and far between.
