let C be category; :: thesis: for D being non empty subcategory of C
for o being object of D
for o9 being object of C st o = o9 holds
idm o = idm o9
let D be non empty subcategory of C; :: thesis: for o being object of D
for o9 being object of C st o = o9 holds
idm o = idm o9
let o be object of D; :: thesis: for o9 being object of C st o = o9 holds
idm o = idm o9
let o9 be object of C; :: thesis: ( o = o9 implies idm o = idm o9 )
assume A1: o = o9 ; :: thesis: idm o = idm o9
then reconsider m = idm o9 as Morphism of o,o by Def14;
A2: idm o9 in <^o,o^> by A1, Def14;

now

let p be object of D; :: thesis: ( <^o,p^> <> {} implies for a being Morphism of o,p holds a * m = a )
assume A3: <^o,p^> <> {} ; :: thesis: for a being Morphism of o,p holds a * m = a
reconsider p9 = p as object of C by Th30;
A4: <^o9,p9^> <> {} by A1, A3, Th32, XBOOLE_1:3;
let a be Morphism of o,p; :: thesis: a * m = a
reconsider n = a as Morphism of o9,p9 by A1, A3, Th34;
thus a * m = n * (idm o9) by A1, A2, A3, Th33
.= a by A4, ALTCAT_1:def 17 ; :: thesis: verum

end;

hence idm o = idm o9 by ALTCAT_1:def 17; :: thesis: verum