.nr _0 \n(c.
.de (z			\" *** begin floating keep
.@D 4 \\$1 \\$2
.@(
.nr ?T 0
..
.de )z			\" *** end floating keep
.sp \\n(zsu
.@)
.rr _0
.if !\\n(?b \
.	nr dn +(\\n(ppu*\\n($ru)/2u+\\n(zsu
.ie ((\\n(dn+\n(.V)>=\\n(.t):(\\n(?a) \
\{\
.	nr ?a 1
.	ds |x |t
.\}
.el \
\{\
.	nr ?b 1
.	nr _b +\\n(dnu
.	ch @f -\\n(_bu
.	ds |x |b
.\}
.da \\*(|x			\" copy to save macro
.nf
.ls 1
.nr ?k 1
\!.if \\\\n(nl>(\\\\n(tm+2v) .ne \\n(dnu-\\n(zsu
.eo
.cc @
@|k				\" and the body
@cc
.ec
.nr ?k 0
.rm |k				\" remove the temp macro
.da
.in 0
.ls 1
.xl \\n($lu
.ev
..
.de @k			\" --- output floating keep
.ev 1
.nf
.ls 1
.in 0
.sp \\n(zsu
.\\$1
.ec
.br
.rm \\$1
.ev
.nr ?T 0
..
.nr c. \n(_0