  The same but different: That might describe two metrics. On the surface
CLASSI may show two metrics are locally equivalent, but buried beneath one may
be a wealth of further structure. This was beautifully described in a paper by
M.A.H. MacCallum in 1998. Here I will illustrate the effect with two flat
metrics -- one describing ordinary Minkowski spacetime and the other describing
a three-parameter family of Gal'tsov-Letelier-Tod spacetimes. I will dig out
the beautiful hidden classical singularity structure of the latter (a structure
first noticed by Tod in 1994) and then show how quantum considerations can
illuminate the riches. I will then discuss how quantum structure can help us
understand classical singularities and metric parameters in a variety of exact
solutions mined from the Exact Solutions book.
