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

theorem
  s <= p implies ].r,s.[ misses [.p,q.]
proof
  assume
A1: s <= p;
  let t;
  assume t in ].r,s.[;
  then t < s by Th4;
  then t < p by A1,XXREAL_0:2;
  hence thesis by Th1;
end;
