Plan 9 from Bell Labs’s /usr/web/sources/contrib/btdn/src/chem/PS-PEmacros
.de PS \" start picture . \" $1 is height, $2 is width, both in inches .if \\$1>0 .sp .35 .in (\\n(.lu-\\$2)/2u .ne \\$1 .. .de PE \" end of picture .in .if \\$1>0 .sp .65 ..
