let C be ConstructorSignature; ( C is standardized iff C is Subsignature of MaxConstrSign )
A1:
the carrier' of MaxConstrSign = {*,non_op} \/ Constructors
by ABCMIZ_1:def 24;
A2:
dom the Arity of MaxConstrSign = the carrier' of MaxConstrSign
by FUNCT_2:def 1;
A3:
dom the ResultSort of MaxConstrSign = the carrier' of MaxConstrSign
by FUNCT_2:def 1;
thus
( C is standardized implies C is Subsignature of MaxConstrSign )
( C is Subsignature of MaxConstrSign implies C is standardized )
assume A16:
C is Subsignature of MaxConstrSign
; C is standardized
let o be OperSymbol of C; ABCMIZ_A:def 1 ( o is constructor implies ( o in Constructors & o `1 = the_result_sort_of o & card ((o `2) `1) = len (the_arity_of o) ) )
assume A17:
( o <> * & o <> non_op )
; ABCMIZ_1:def 11 ( o in Constructors & o `1 = the_result_sort_of o & card ((o `2) `1) = len (the_arity_of o) )
( the carrier' of C c= the carrier' of MaxConstrSign & o in the carrier' of C )
by A16, INSTALG1:10;
then reconsider c = o as OperSymbol of MaxConstrSign ;
A18:
c is constructor
by A17, ABCMIZ_1:def 11;
not c in {*,non_op}
by A17, TARSKI:def 2;
hence
o in Constructors
by A1, XBOOLE_0:def 3; ( o `1 = the_result_sort_of o & card ((o `2) `1) = len (the_arity_of o) )
thus o `1 =
the ResultSort of MaxConstrSign . c
by A18, ABCMIZ_1:def 24
.=
( the ResultSort of MaxConstrSign | the carrier' of C) . o
by FUNCT_1:49
.=
the ResultSort of C . o
by A16, INSTALG1:12
.=
the_result_sort_of o
; card ((o `2) `1) = len (the_arity_of o)
thus card ((o `2) `1) =
card ( the Arity of MaxConstrSign . c)
by A18, ABCMIZ_1:def 24
.=
card (( the Arity of MaxConstrSign | the carrier' of C) . o)
by FUNCT_1:49
.=
card ( the Arity of C . o)
by A16, INSTALG1:12
.=
len (the_arity_of o)
; verum