let X be set ; :: thesis: for Y being complex-functions-membered set
for f being PartFunc of X,Y
for g being complex-valued Function holds <-> (f <-> g) = (<-> f) <+> g

let Y be complex-functions-membered set ; :: thesis: for f being PartFunc of X,Y
for g being complex-valued Function holds <-> (f <-> g) = (<-> f) <+> g

let f be PartFunc of X,Y; :: thesis: for g being complex-valued Function holds <-> (f <-> g) = (<-> f) <+> g
let g be complex-valued Function; :: thesis: <-> (f <-> g) = (<-> f) <+> g
set f1 = f <-> g;
set f2 = <-> f;
A1: dom (<-> (f <-> g)) = dom (f <-> g) by Def33;
A2: ( dom (f <-> g) = (dom f) /\ (dom g) & dom (<-> f) = dom f ) by ;
hence A3: dom (<-> (f <-> g)) = dom ((<-> f) <+> g) by ; :: according to FUNCT_1:def 11 :: thesis: for b1 being object holds
( not b1 in dom (<-> (f <-> g)) or (<-> (f <-> g)) . b1 = ((<-> f) <+> g) . b1 )

let x be object ; :: thesis: ( not x in dom (<-> (f <-> g)) or (<-> (f <-> g)) . x = ((<-> f) <+> g) . x )
assume A4: x in dom (<-> (f <-> g)) ; :: thesis: (<-> (f <-> g)) . x = ((<-> f) <+> g) . x
then A5: x in dom (<-> f) by ;
thus (<-> (f <-> g)) . x = - ((f <-> g) . x) by
.= - ((f . x) - (g . x)) by A1, A4, Th62
.= (- (f . x)) + (g . x) by Th11
.= ((<-> f) . x) + (g . x) by
.= ((<-> f) <+> g) . x by ; :: thesis: verum