 reserve a,x for Real;
 reserve n for Element of NAT;
 reserve A for non empty closed_interval Subset of REAL;
 reserve f,h,f1,f2 for PartFunc of REAL,REAL;
 reserve Z for open Subset of REAL;

theorem
 A c= Z & (for x st x in Z holds f1.x=1) & f=arccot/(f1+#Z 2)
 & Z c= ]. -1,1 .[ & Z c= dom (( #Z 2)*(arccot))
 & Z = dom f & f|A is continuous implies
 integral(f,A)=(-(1/2)(#)(( #Z 2)*(arccot))).(upper_bound A)
              -(-(1/2)(#)(( #Z 2)*(arccot))).(lower_bound A)
proof
  assume
A1:A c= Z & (for x st x in Z holds f1.x=1) & f=arccot/(f1+#Z 2)
   & Z c= ]. -1,1 .[ & Z c= dom (( #Z 2)*(arccot))
   & Z = dom f & f|A is continuous;then
A2:f is_integrable_on A & f|A is bounded by INTEGRA5:10,11;
A3:-(1/2)(#)(( #Z 2)*(arccot)) is_differentiable_on Z by A1,Th44;
   Z c= dom (arccot) /\ (dom (f1+#Z 2) \ (f1+#Z 2)"{0})
   by A1,RFUNCT_1:def 1;then
Z c= dom (f1+#Z 2) \ (f1+#Z 2)"{0} by XBOOLE_1:18;
then A4:Z c= dom ((f1+#Z 2)^) by RFUNCT_1:def 2;
   dom ((f1+#Z 2)^) c= dom (f1+#Z 2) by RFUNCT_1:1;then
A5:Z c= dom (f1+#Z 2) by A4;
A6:for x st x in Z holds f.x=arccot.x / (1+x^2)
   proof
   let x;
   assume
A7:x in Z;then
   (arccot/(f1+#Z 2)).x =arccot.x/(f1+#Z 2).x by A1,RFUNCT_1:def 1
   .=arccot.x/(f1.x+(( #Z 2).x)) by A5,A7,VALUED_1:def 1
   .=arccot.x/(f1.x+(x #Z 2)) by TAYLOR_1:def 1
   .=arccot.x/(1+(x #Z 2)) by A1,A7
   .=arccot.x / (1+x^2) by FDIFF_7:1;
    hence thesis by A1;
    end;
A8:for x being Element of REAL st x in dom((-(1/2)(#)(( #Z 2)*(arccot)))`|Z)
   holds
   ((-(1/2)(#)(( #Z 2)*(arccot)))`|Z).x=f.x
   proof
   let x be Element of REAL;
   assume x in dom((-(1/2)(#)(( #Z 2)*(arccot)))`|Z);then
A9:x in Z by A3,FDIFF_1:def 7;then
  ((-(1/2)(#)(( #Z 2)*(arccot)))`|Z).x=arccot.x / (1+x^2) by A1,Th44
  .=f.x by A6,A9;
  hence thesis;
  end;
  dom((-(1/2)(#)(( #Z 2)*(arccot)))`|Z)=dom f by A1,A3,FDIFF_1:def 7;
  then((-(1/2)(#)(( #Z 2)*(arccot)))`|Z)= f by A8,PARTFUN1:5;
  hence thesis by A1,A2,Th44,INTEGRA5:13;
end;
