Seqn is a version of eqn modified for sroff and the Sanders Media 12/7
printer.  In general the defaults, etc. are similar to eqn but it
is limited to the special symbols in the Sci/Pi and greek/Math fonts.
The default font for non-special tokens is font 2 (Italic); this is 
a problem if font 2 is underlined instead of italic.  To turn off
underlining in font 2, insert ".uf 0" in the input.  ".ul" will still
produce underlined text if desired.
You can also make the default font for equation characters be font 1
with the lines:
.EQ
gfont 1
.EN
in the text.