let X be non empty set ; :: thesis: for S being SigmaField of X
for f being PartFunc of X,ExtREAL
for A being Element of S st f is_measurable_on A & A c= dom f holds
A /\ (eq_dom f,+infty ) in S
let S be SigmaField of X; :: thesis: for f being PartFunc of X,ExtREAL
for A being Element of S st f is_measurable_on A & A c= dom f holds
A /\ (eq_dom f,+infty ) in S
let f be PartFunc of X,ExtREAL ; :: thesis: for A being Element of S st f is_measurable_on A & A c= dom f holds
A /\ (eq_dom f,+infty ) in S
let A be Element of S; :: thesis: ( f is_measurable_on A & A c= dom f implies A /\ (eq_dom f,+infty ) in S )
assume that
A1: f is_measurable_on A and
A2: A c= dom f ; :: thesis: A /\ (eq_dom f,+infty ) in S
defpred S₁[ Element of NAT , set ] means A /\ (great_dom f,(R_EAL $1)) = $2;
A3: for n being Element of NAT ex y being Element of S st S₁[n,y]

proof

let n be Element of NAT ; :: thesis: ex y being Element of S st S₁[n,y]
reconsider y = A /\ (great_dom f,(R_EAL n)) as Element of S by A1, A2, Th33;
take y ; :: thesis: S₁[n,y]
thus S₁[n,y] ; :: thesis: verum

end;

consider F being Function of NAT ,S such that
A4: for n being Element of NAT holds S₁[n,F . n] from FUNCT_2:sch 3(A3);
A /\ (eq_dom f,+infty ) = meet (rng F) by A4, Th27;
hence A /\ (eq_dom f,+infty ) in S ; :: thesis: verum