Wigner's theorem is a fundamental part of the mathematical formulation
of quantum mechanics. The theorem characterizes unitary and anti-unitary
operators as symmetries of quantum mechanical systems, and is a key
result when relating preserver problems to quantum mechanics. At the
heart of this book is a geometric approach to Wigner-type theorems,
unifying both classical and more recent results. Readers are initiated
in a wide range of topics from geometric transformations of
Grassmannians to lattices of closed subspaces, before moving on to a
discussion of applications. An introduction to all the key aspects of
the basic theory is included as are plenty of examples, making this book
a useful resource for beginning graduate students and non-experts, as
well as a helpful reference for specialist researchers.