#once #create message
.ND
.tr %$
.EQ
delim $$
.EN
.LP
The next step is to learn about "diacriticals", which
is a big word for funny marks on symbols, like
a bar over something ($x bar$), or a tilde or hat on
something ($x tilde ,~a hat$), or perhaps a dot 
or dotdot ($T dot ,~U dotdot$), or even an
underlining like $abc under$.

These are all easy.  Each funny character
has a name, and all you have to do is put the name
after the thing you want the character on.
Thus
  x hat makes $x hat$
  y bar makes $y bar$
  T dot makes $T dot$
  x tilde makes $x tilde$ (notice that we spell tilde)
  u dotdot makes $u dotdot$ (looks ugly on a terminal)
.br
and
  i under makes $i under$.

Except for "bar" and "under", these are almost always
attached to just a single letter.
If you want to put a bar over something longer, like
${2 pi +1} bar$, simply enclose the thing in braces:

  {2 pi +1} bar

Modify "Example" to produce output that looks like this,
then type "ready".
.pl 1
#once #create Ref
.EQ
delim $$
.EN
.LP
Let $x bar$, $y bar$, and $z bar$ be the components of $pi bar$.
Let ${alpha +1} bar$ be the mean value of $alpha hat$.
.pl 1
#once #create Example
.EQ
delim $$
.EN
.LP
Let x bar, y bar, and z bar be the components of pi bar.
Let alpha +1 bar be the mean value of alpha hat.
.pl 1
#
#once neqn Ref | nroff >X1 &
#once neqn message Ref | nroff -T$term %s/tinyms -
#user
neqn Example | nroff >X2
#cmp X1 X2
#fail
Don't forget to set delimiters at the beginning,
and get the spaces right around the dollar signs.
#log
#next
9.1b 10
9.2a 5