A student asked if an object whose density is just less than than needed
for a black hole could _look_ like a black hole to an observer in a
reference frame moving at near the speed of light relative to the object's
inertial reference frame, due to relativistic mass increase. Could it be a
black hole to some observers and not to others?
Another student asked if General Relativity is a superset of Special
Relativity; i.e., can all the results of SR be derived as special cases
from GR? After all, aren't inertial reference frames just special cases of
accelerated reference frames (where a = 0)?