The mishna [makos 6a] says that if two witnesses view
an act from one window and two from another window they combine to form one set
of witnesses.
The Beis Yosef [195] says that if people ate a meal
and there is a reshus ha-rabbim in between them they may not join together to
form a zimmun. Why is that different from the witnesses where there is a reshus
harabbim in between them and they do join to form one set of witnesses?
