theorem
  dom f = A implies (f is B-measurable iff f is (A/\B)-measurable)
proof
  assume
A1: dom f = A;
  then
A2: dom Re f = A by COMSEQ_3:def 3;
A3: dom Im f = A by A1,COMSEQ_3:def 4;
  hence f is B-measurable implies f is (A/\B)-measurable by A2,MESFUNC6:80;
  thus thesis by A2,A3,MESFUNC6:80;
end;
