Use align environment instead of equation everywhere
Fix the overflowing of footnotes in the appendices
Typo
The definition of n and the matrix P were incompatible
I had forgotten minus signs in Debye-Waller factors
Do not refer to the twin law as a symmetry operator

As it is not an element of the group of symmetries
In the twinning section, h was not a row vector
Put that eqn on one line to get rid of the orphan section 3 title

This also improves the amount of white space in the right column on that
page.
Put back the text of most footnotes inside the main body

Two reasons. First, we abused footnotes too much and then the iUCR style
does not get the page layout right, which results in footnotes overflowing
on top of the main body of text.