set.mm: Add Metamath 100 markings for 50..77
set.mm: Add Metamath 100 markings for 50..77

Add more markings in set.mm. Again, this is *not* rewrapped (yet).

Signed-off-by: David A. Wheeler <9ae72d22d8b894b865a7a496af4fab6320e6abb2@dwheeler.com>

metamath/set.mm,metamath/set.mm,metamath/set.mm