. \"DS - display. If .DS C, center; L, left-adjust; I, indent.
.if \\n(VS>40 .vs \\n(VSu
.if \\n(VS<=39 .vs \\n(VSp
.if \\n(.$ .if !"\\$1"I" .if !"\\$1"" .in \\n(OIu
.if \\n(.$ .if !"\\$1"I" .if !"\\$1"" .in +\\$1n
.de BD \" block display: save everything, then center it.
.de DF \" finish a block display to be recentered.
.if \\n(dl>\\n(BD .nr BD \\n(dl
.if \\n(BD<\\n(.l .in (\\n(.lu-\\n(BDu)/2u