.de sh			*** section heading
.if \\n(.$ .@d \\$1
.ds @@ #\\n(#0
.nr \\*(@@ +1
.ds @n \\n(#1
.if \\n(#2 .as @n .\\n(#2
.if \\n(#3 .as @n .\\n(#3
.if \\n(#4 .as @n .\\n(#4
.if \\n(#5 .as @n .\\n(#5
.if \\n(#6 .as @n .\\n(#6
.if !\\n(#0 .in 0
.if \\n(#0 .@p
..
.de @d			change section depth
.nr #0 \\$1
.if \\n(#0 .if !\\n(#1 .nr #1 0
.if !\\n(#0 .nr #1 0
.if \\n(#0-1 .if !\\n(#2 .nr #2 0
.if !\\n(#0-1 .nr #2 0
.if \\n(#0-2 .if !\\n(#3 .nr #3 0
.if !\\n(#0-2 .nr #3 0
.if \\n(#0-3 .if !\\n(#4 .nr #4 0
.if !\\n(#0-3 .nr #4 0
.if \\n(#0-4 .if !\\n(#5 .nr #5 0
.if !\\n(#0-4 .nr #5 0
.if \\n(#0-5 .if !\\n(#6 .nr #6 0
.if !\\n(#0-5 .nr #6 0
..
.de @p			print section heading
.in \\n(#i*\\n(#0u
.sp
.ti -\\n(#i
\\*(@n\&.\ \ \c
..
.de up			*** move up heading number (2.1.1 -> 2.2)
.sh -1
..
.de ux			*** heading up, no increment (2.1.1 -> 2.1)
.nr _9 \\n(#0-1
.if \\n(.$ .nr _9 +1
.if \\n(.$ .nr _9 \\$1
.@d \\n(_9
.in \\n(#i*\\n(#0u
..
.de dn			*** move down heading number (2.1.1 -> 2.1.1.1)
.sh +1
..
.de gs			*** get section number
.ds ,\\$1 \\*(@n
..
.nr #i 4
.de PS			*** space after a section title
.sp 1
..
.po 5
.de @h
'sp 3
'tl \\*(HE
'sp 2
..
.de @f
'bp
..
.wh 0 @h
.wh -6 @f