ssp \- limit to single spacing
compresses consecutive blank lines to at most one blank line to produce
more compact output for a \s-2CRT\s0 or to save paper on the printer.
is even more zealous, getting rid of all empty lines.
is useful for compressing text with blank lines onto a \s-2CRT\s0,
colcrt(UCB), cr3(UCB), man(UCB)