The words about double spacing quoted below can be misread as unconditional advice. I suggest replacing "In" with "In this case".
Also so much mention of AT&T strikes me as clutter. At least the first instance would better be dropped. "If a second argument is never given to the 'ss' request, GNU 'troff' separates sentences as AT&T 'troff' does. In input to GNU 'troff', as with AT&T 'troff', a sentence should always be followed by either a newline or two spaces." Doug
