As these guides are created for groff, I cannot guarantee
that they are applicable to troff. If you use troff
and can confirm them to work for it – please let me know.
Apart from groff, these guides may include other programs
used together with groff, such as eqn, tbl,
and so on. I will try to make this clear in the description of each
Collection of papers on troff and its companions
Following is a collection based on troff.org/papers. However,
I found that much of the links referenced from that site are dead.
I have instead downloaded and compiled pdfs from archive.org. Much
of the material available was written at Bell Labs. The CSTR
documents below refer to ’Computer Science Technical Reports’, a
Bell Labs internal numbering system used in the past.
In the man page of eqn you can read about defining
a macro for canceling an expression. This macro draws a line over
the expression, as an indication it’s canceled. When using paper
and pen I usually use a cross instead, so this is how you do the
same in eqn.