let C be non empty set ; :: thesis: for V being RealNormSpace
for f1, f2 being PartFunc of C,the carrier of V
for f3 being PartFunc of C,REAL holds (f3 (#) f1) - (f3 (#) f2) = f3 (#) (f1 - f2)
let V be RealNormSpace; :: thesis: for f1, f2 being PartFunc of C,the carrier of V
for f3 being PartFunc of C,REAL holds (f3 (#) f1) - (f3 (#) f2) = f3 (#) (f1 - f2)
let f1, f2 be PartFunc of C,the carrier of V; :: thesis: for f3 being PartFunc of C,REAL holds (f3 (#) f1) - (f3 (#) f2) = f3 (#) (f1 - f2)
let f3 be PartFunc of C,REAL ; :: thesis: (f3 (#) f1) - (f3 (#) f2) = f3 (#) (f1 - f2)
A1: dom ((f3 (#) f1) - (f3 (#) f2)) = (dom (f3 (#) f1)) /\ (dom (f3 (#) f2)) by Def2
.= (dom (f3 (#) f1)) /\ ((dom f3) /\ (dom f2)) by Def3
.= ((dom f3) /\ (dom f1)) /\ ((dom f3) /\ (dom f2)) by Def3
.= ((dom f3) /\ ((dom f3) /\ (dom f1))) /\ (dom f2) by XBOOLE_1:16
.= (((dom f3) /\ (dom f3)) /\ (dom f1)) /\ (dom f2) by XBOOLE_1:16
.= (dom f3) /\ ((dom f1) /\ (dom f2)) by XBOOLE_1:16
.= (dom f3) /\ (dom (f1 - f2)) by Def2
.= dom (f3 (#) (f1 - f2)) by Def3 ;

now

let c be Element of C; :: thesis: ( c in dom (f3 (#) (f1 - f2)) implies (f3 (#) (f1 - f2)) /. c = ((f3 (#) f1) - (f3 (#) f2)) /. c )
assume A2: c in dom (f3 (#) (f1 - f2)) ; :: thesis: (f3 (#) (f1 - f2)) /. c = ((f3 (#) f1) - (f3 (#) f2)) /. c
then c in (dom (f3 (#) f1)) /\ (dom (f3 (#) f2)) by A1, Def2;
then A3: ( c in dom (f3 (#) f1) & c in dom (f3 (#) f2) ) by XBOOLE_0:def 4;
c in (dom f3) /\ (dom (f1 - f2)) by A2, Def3;
then A4: c in dom (f1 - f2) by XBOOLE_0:def 4;
thus (f3 (#) (f1 - f2)) /. c = (f3 . c) * ((f1 - f2) /. c) by A2, Def3
.= (f3 . c) * ((f1 /. c) - (f2 /. c)) by A4, Def2
.= ((f3 . c) * (f1 /. c)) - ((f3 . c) * (f2 /. c)) by RLVECT_1:48
.= ((f3 (#) f1) /. c) - ((f3 . c) * (f2 /. c)) by A3, Def3
.= ((f3 (#) f1) /. c) - ((f3 (#) f2) /. c) by A3, Def3
.= ((f3 (#) f1) - (f3 (#) f2)) /. c by A1, A2, Def2 ; :: thesis: verum

end;

hence (f3 (#) f1) - (f3 (#) f2) = f3 (#) (f1 - f2) by A1, PARTFUN2:3; :: thesis: verum