I found an outline that I’ve never seen, nor can I find it in any dictionaries. It appears to be a dis-joined right-s prefix (i.e., ‘super’) over th(r)-s. I saw it in Gregg Speed studies 3rd ed. on page 363, third line down. The sentence makes sense without the ‘s’, but it seems to be written in the plate and not a printing smudge. Any ideas?
(by Michael for group greggshorthand)