public forums:
(a)    two types:
(b)    true public forum (I)
(i)    these are public forums by custom & tradition, not b/c of any gov’t policy; streets, sidewalks and parks
(c)    designated public forum (II)
(i)    places gov’t has decided to open up to the public (a broad range of ppl)
(ii)    these follow same rules, except the gov’t can change its mind