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

theorem :: MEASURE6:36
  ].p,-infty.] = {}
proof
  not ex x being object st x in ].p,-infty.]
  proof
    given x being object such that
A1: x in ].p,-infty.];
    reconsider s = x as ExtReal by A1;
A2: p < s by A1,Th2;
    s <= -infty by A1,Th2;
    then p < -infty by A2,XXREAL_0:2;
    hence contradiction by XXREAL_0:5;
  end;
  hence thesis;
end;
