:: More on Divisibility Criteria for Selected Primes
:: by Adam Naumowicz and Rados{\l}aw Piliszek
::
:: Received May 19, 2013
:: Copyright (c) 2013-2021 Association of Mizar Users
theorem
Th1
:
:: NUMERAL2:1
for
f
being non
empty
XFinSequence
holds
f
|
1
=
<%
(
f
.
0
)
%>
proof
end;
theorem
Th2
:
:: NUMERAL2:2
for
f
being non
empty
XFinSequence
holds
f
=
<%
(
f
.
0
)
%>
^
(
f
/^
1
)
proof
end;
theorem
Th3
:
:: NUMERAL2:3
for
f
being
XFinSequence
holds
mid
(
f
,2,
(
len
f
)
)
=
f
/^
1
proof
end;
theorem
Th4
:
:: NUMERAL2:4
for
X
,
Y
being
finite
natural-membered
set
st
X
misses
Y
holds
dom
(
(
Sgm0
X
)
^
(
Sgm0
Y
)
)
=
dom
(
Sgm0
(
X
\/
Y
)
)
proof
end;
theorem
Th5
:
:: NUMERAL2:5
for
X
,
Y
being
finite
natural-membered
set
holds
rng
(
(
Sgm0
X
)
^
(
Sgm0
Y
)
)
=
rng
(
Sgm0
(
X
\/
Y
)
)
proof
end;
theorem
Th6
:
:: NUMERAL2:6
for
F
being
XFinSequence
for
X
being
set
holds
dom
(
SubXFinS
(
F
,
X
)
)
=
dom
(
Sgm0
(
X
/\
(
dom
F
)
)
)
proof
end;
definition
redefine
func
EvenNAT
equals
:: NUMERAL2:def 1
{
n
where
n
is
Nat
:
n
is
even
}
;
compatibility
for
b
1
being
Element
of
K37
(
omega
) holds
(
b
1
=
EvenNAT
iff
b
1
=
{
n
where
n
is
Nat
:
n
is
even
}
)
proof
end;
end;
::
deftheorem
defines
EvenNAT
NUMERAL2:def 1 :
EvenNAT
=
{
n
where
n
is
Nat
:
n
is
even
}
;
definition
redefine
func
OddNAT
equals
:: NUMERAL2:def 2
{
n
where
n
is
Nat
:
n
is
odd
}
;
compatibility
for
b
1
being
Element
of
K37
(
omega
) holds
(
b
1
=
OddNAT
iff
b
1
=
{
n
where
n
is
Nat
:
n
is
odd
}
)
proof
end;
end;
::
deftheorem
defines
OddNAT
NUMERAL2:def 2 :
OddNAT
=
{
n
where
n
is
Nat
:
n
is
odd
}
;
theorem
Th7
:
:: NUMERAL2:7
EvenNAT
misses
OddNAT
proof
end;
theorem
Th8
:
:: NUMERAL2:8
EvenNAT
\/
OddNAT
=
NAT
proof
end;
registration
let
F
be
Sequence
;
let
P
be
Permutation
of
(
dom
F
)
;
cluster
P
(#)
F
->
Sequence-like
;
correctness
coherence
F
*
P
is
Sequence-like
;
proof
end;
end;
theorem
Th9
:
:: NUMERAL2:9
for
F
being
XFinSequence
for
X
,
Y
being
set
st
X
misses
Y
holds
ex
P
being
Permutation
of
(
dom
(
SubXFinS
(
F
,
(
X
\/
Y
)
)
)
)
st
(
SubXFinS
(
F
,
(
X
\/
Y
)
)
)
*
P
=
(
SubXFinS
(
F
,
X
)
)
^
(
SubXFinS
(
F
,
Y
)
)
proof
end;
theorem
Th10
:
:: NUMERAL2:10
for
cF
being
complex-valued
XFinSequence
for
B1
,
B2
being
set
st
B1
misses
B2
holds
Sum
(
SubXFinS
(
cF
,
(
B1
\/
B2
)
)
)
=
(
Sum
(
SubXFinS
(
cF
,
B1
)
)
)
+
(
Sum
(
SubXFinS
(
cF
,
B2
)
)
)
proof
end;
theorem
Th11
:
:: NUMERAL2:11
for
F
being
XFinSequence
holds
F
=
SubXFinS
(
F
,
NAT
)
proof
end;
theorem
Th12
:
:: NUMERAL2:12
for
N
,
i
being
Nat
st
i
in
dom
(
Sgm0
(
N
/\
EvenNAT
)
)
holds
(
Sgm0
(
N
/\
EvenNAT
)
)
.
i
=
2
*
i
proof
end;
theorem
Th13
:
:: NUMERAL2:13
for
N
,
i
being
Nat
st
i
in
dom
(
Sgm0
(
N
/\
OddNAT
)
)
holds
(
Sgm0
(
N
/\
OddNAT
)
)
.
i
=
(
2
*
i
)
+
1
proof
end;
theorem
Th14
:
:: NUMERAL2:14
for
i
,
j
being
Integer
holds
(
i
mod
j
)
mod
j
=
i
mod
j
proof
end;
theorem
:: NUMERAL2:15
for
i
,
j
,
k
,
l
being
Integer
st
i
mod
l
=
j
mod
l
holds
(
k
+
i
)
mod
l
=
(
k
+
j
)
mod
l
proof
end;
theorem
Th16
:
:: NUMERAL2:16
for
d
being
XFinSequence
of
INT
for
n
being
Integer
st ( for
i
being
Nat
st
i
in
dom
d
holds
n
divides
d
.
i
) holds
n
divides
Sum
d
proof
end;
theorem
:: NUMERAL2:17
for
d
,
e
being
XFinSequence
of
INT
for
n
being
Integer
st
dom
d
=
dom
e
& ( for
i
being
Nat
st
i
in
dom
d
holds
e
.
i
=
(
d
.
i
)
mod
n
) holds
(
Sum
d
)
mod
n
=
(
Sum
e
)
mod
n
proof
end;
theorem
Th18
:
:: NUMERAL2:18
for
f
,
g
being
XFinSequence
of
NAT
for
i
being
Integer
st
dom
f
=
dom
g
& ( for
n
being
object
st
n
in
dom
f
holds
f
.
n
=
i
*
(
g
.
n
)
) holds
Sum
f
=
i
*
(
Sum
g
)
proof
end;
theorem
Th19
:
:: NUMERAL2:19
for
n
,
b
being
Nat
st
b
>
1 holds
n
=
(
b
*
(
value
(
(
mid
(
(
digits
(
n
,
b
)
)
,2,
(
len
(
digits
(
n
,
b
)
)
)
)
)
,
b
)
)
)
+
(
(
digits
(
n
,
b
)
)
.
0
)
proof
end;
theorem
Th20
:
:: NUMERAL2:20
for
n
,
k
being
Nat
st
k
=
(
10
|^
(
2
*
n
)
)
-
1 holds
11
divides
k
proof
end;
theorem
Th21
:
:: NUMERAL2:21
for
n
,
k
being
Nat
st
k
=
(
10
|^
(
(
2
*
n
)
+
1
)
)
+
1 holds
11
divides
k
proof
end;
theorem
Th22
:
:: NUMERAL2:22
7,10
are_coprime
proof
end;
theorem
Th23
:
:: NUMERAL2:23
29 is
prime
proof
end;
theorem
Th24
:
:: NUMERAL2:24
31 is
prime
proof
end;
theorem
Th25
:
:: NUMERAL2:25
41 is
prime
proof
end;
theorem
Th26
:
:: NUMERAL2:26
47 is
prime
proof
end;
theorem
Th27
:
:: NUMERAL2:27
53 is
prime
proof
end;
theorem
Th28
:
:: NUMERAL2:28
59 is
prime
proof
end;
theorem
Th29
:
:: NUMERAL2:29
61 is
prime
proof
end;
theorem
Th30
:
:: NUMERAL2:30
67 is
prime
proof
end;
theorem
Th31
:
:: NUMERAL2:31
71 is
prime
proof
end;
theorem
Th32
:
:: NUMERAL2:32
73 is
prime
proof
end;
theorem
Th33
:
:: NUMERAL2:33
79 is
prime
proof
end;
theorem
Th34
:
:: NUMERAL2:34
89 is
prime
proof
end;
theorem
Th35
:
:: NUMERAL2:35
97 is
prime
proof
end;
theorem
Th36
:
:: NUMERAL2:36
101 is
prime
proof
end;
theorem
Th37
:
:: NUMERAL2:37
for
p
being
prime
Nat
for
n
,
f
,
b
being
Nat
st ex
k
being
Nat
st
(
b
*
f
)
+
1
=
p
*
k
&
b
>
1 &
p
,
b
are_coprime
holds
(
p
divides
n
iff
p
divides
(
value
(
(
mid
(
(
digits
(
n
,
b
)
)
,2,
(
len
(
digits
(
n
,
b
)
)
)
)
)
,
b
)
)
-
(
f
*
(
(
digits
(
n
,
b
)
)
.
0
)
)
)
proof
end;
theorem
Th38
:
:: NUMERAL2:38
for
p
being
prime
Nat
for
n
,
f
,
b
being
Nat
st ex
k
being
Nat
st
(
b
*
f
)
-
1
=
p
*
k
&
b
>
1 &
p
,
b
are_coprime
holds
(
p
divides
n
iff
p
divides
(
value
(
(
mid
(
(
digits
(
n
,
b
)
)
,2,
(
len
(
digits
(
n
,
b
)
)
)
)
)
,
b
)
)
+
(
f
*
(
(
digits
(
n
,
b
)
)
.
0
)
)
)
proof
end;
::
Divisibility rule#Divisibility by 7
theorem
Th39
:
:: NUMERAL2:39
for
n
being
Nat
holds
( 7
divides
n
iff 7
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
2
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:40
for
n
being
Nat
holds
( 7
divides
n
iff 7
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
2
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th41
:
:: NUMERAL2:41
for
n
being
Nat
holds
( 11
divides
n
iff 11
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
(
digits
(
n
,10)
)
.
0
)
)
proof
end;
theorem
:: NUMERAL2:42
for
n
being
Nat
holds
( 11
divides
n
iff 11
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
(
digits
(
n
,10)
)
.
0
)
)
proof
end;
::
Divisibility rule#Divisibility by 11
theorem
:: NUMERAL2:43
for
n
being
Nat
holds
( 11
divides
n
iff 11
divides
(
Sum
(
SubXFinS
(
(
digits
(
n
,10)
)
,
EvenNAT
)
)
)
-
(
Sum
(
SubXFinS
(
(
digits
(
n
,10)
)
,
OddNAT
)
)
)
)
proof
end;
::
Divisibility rule#Divisibility by 13
theorem
Th44
:
:: NUMERAL2:44
for
n
being
Nat
holds
( 13
divides
n
iff 13
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
4
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:45
for
n
being
Nat
holds
( 13
divides
n
iff 13
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
4
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th46
:
:: NUMERAL2:46
for
n
being
Nat
holds
( 17
divides
n
iff 17
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
5
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:47
for
n
being
Nat
holds
( 17
divides
n
iff 17
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
5
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th48
:
:: NUMERAL2:48
for
n
being
Nat
holds
( 19
divides
n
iff 19
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
2
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:49
for
n
being
Nat
holds
( 19
divides
n
iff 19
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
2
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th50
:
:: NUMERAL2:50
for
n
being
Nat
holds
( 23
divides
n
iff 23
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
7
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:51
for
n
being
Nat
holds
( 23
divides
n
iff 23
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
7
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th52
:
:: NUMERAL2:52
for
n
being
Nat
holds
( 29
divides
n
iff 29
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
3
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:53
for
n
being
Nat
holds
( 29
divides
n
iff 29
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
3
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th54
:
:: NUMERAL2:54
for
n
being
Nat
holds
( 31
divides
n
iff 31
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
3
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:55
for
n
being
Nat
holds
( 31
divides
n
iff 31
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
3
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th56
:
:: NUMERAL2:56
for
n
being
Nat
holds
( 37
divides
n
iff 37
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
11
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:57
for
n
being
Nat
holds
( 37
divides
n
iff 37
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
11
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th58
:
:: NUMERAL2:58
for
n
being
Nat
holds
( 41
divides
n
iff 41
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
4
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:59
for
n
being
Nat
holds
( 41
divides
n
iff 41
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
4
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th60
:
:: NUMERAL2:60
for
n
being
Nat
holds
( 43
divides
n
iff 43
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
13
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:61
for
n
being
Nat
holds
( 43
divides
n
iff 43
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
13
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th62
:
:: NUMERAL2:62
for
n
being
Nat
holds
( 47
divides
n
iff 47
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
14
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:63
for
n
being
Nat
holds
( 47
divides
n
iff 47
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
14
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th64
:
:: NUMERAL2:64
for
n
being
Nat
holds
( 53
divides
n
iff 53
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
16
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:65
for
n
being
Nat
holds
( 53
divides
n
iff 53
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
16
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th66
:
:: NUMERAL2:66
for
n
being
Nat
holds
( 59
divides
n
iff 59
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
6
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:67
for
n
being
Nat
holds
( 59
divides
n
iff 59
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
6
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th68
:
:: NUMERAL2:68
for
n
being
Nat
holds
( 61
divides
n
iff 61
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
6
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:69
for
n
being
Nat
holds
( 61
divides
n
iff 61
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
6
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th70
:
:: NUMERAL2:70
for
n
being
Nat
holds
( 67
divides
n
iff 67
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
20
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:71
for
n
being
Nat
holds
( 67
divides
n
iff 67
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
20
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th72
:
:: NUMERAL2:72
for
n
being
Nat
holds
( 71
divides
n
iff 71
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
7
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:73
for
n
being
Nat
holds
( 71
divides
n
iff 71
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
7
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th74
:
:: NUMERAL2:74
for
n
being
Nat
holds
( 73
divides
n
iff 73
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
22
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:75
for
n
being
Nat
holds
( 73
divides
n
iff 73
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
22
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th76
:
:: NUMERAL2:76
for
n
being
Nat
holds
( 79
divides
n
iff 79
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
8
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:77
for
n
being
Nat
holds
( 79
divides
n
iff 79
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
8
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th78
:
:: NUMERAL2:78
for
n
being
Nat
holds
( 83
divides
n
iff 83
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
25
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:79
for
n
being
Nat
holds
( 83
divides
n
iff 83
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
25
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th80
:
:: NUMERAL2:80
for
n
being
Nat
holds
( 89
divides
n
iff 89
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
+
(
9
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:81
for
n
being
Nat
holds
( 89
divides
n
iff 89
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
+
(
9
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th82
:
:: NUMERAL2:82
for
n
being
Nat
holds
( 97
divides
n
iff 97
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
29
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:83
for
n
being
Nat
holds
( 97
divides
n
iff 97
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
29
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
Th84
:
:: NUMERAL2:84
for
n
being
Nat
holds
( 101
divides
n
iff 101
divides
(
value
(
(
mid
(
(
digits
(
n
,10)
)
,2,
(
len
(
digits
(
n
,10)
)
)
)
)
,10)
)
-
(
10
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;
theorem
:: NUMERAL2:85
for
n
being
Nat
holds
( 101
divides
n
iff 101
divides
(
value
(
(
(
digits
(
n
,10)
)
/^
1
)
,10)
)
-
(
10
*
(
(
digits
(
n
,10)
)
.
0
)
)
)
proof
end;