reserve x for set,
  p,q,r,s,t,u for ExtReal,
  g for Real,
  a for Element of ExtREAL;

theorem Th16:
  x in ].p,q.[ implies x in [.p,q.] & x <> p & x <> q
proof
  assume
A1: x in ].p,q.[;
  then x in ].p,q.] by Th15;
  hence thesis by A1,Th12,Th15;
end;
