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

theorem
  for s being Real holds
  ].-infty,+infty.] \ [.p,s.] = ].-infty,p.[ \/ ].s,+infty.]
  by Th340,XXREAL_0:3;
