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

theorem :: MEASURE5:12,15
  p <= q implies ].q,p.] = {}
proof
  assume
A1: p <= q;
  assume ].q,p.] <> {};
  then consider r such that
A2: r in ].q,p.];
A3: q < r by A2,Th2;
  r <= p by A2,Th2;
  hence contradiction by A1,A3,XXREAL_0:2;
end;
