ref: 3d5dca521797b5a91ebc4281fbaf58211bb4f40f dir: /sys/lib/troff/font/devutf/charlib/bx/
/build_bx { pop size 2 div /side exch def currentpoint newpath moveto 0 side rlineto side 0 rlineto 0 side neg rlineto closepath fill } def