The natural number 90 as a set
For natural numbers, the
Von Neumann definition
is usually used: A natural number N then is the set of all lower natural
numbers, with 0 being the empty set.
N1 < N2 is defined as
N1 ∈ N2 .
N + 1 is defined as N ∪ { N }.
N + 0 is defined as N.
N1 + (N2 + 1) is defined as
(N1 + N2 ) + 1.
90 = {
0
,
1
,
2
,
3
,
4
,
5
,
6
,
7
,
8
,
9
,
10
,
11
,
12
,
13
,
14
,
15
,
16
,
17
,
18
,
19
,
20
,
21
,
22
,
23
,
24
,
25
,
26
,
27
,
28
,
29
,
30
,
31
,
32
,
33
,
34
,
35
,
36
,
37
,
38
,
39
,
40
,
41
,
42
,
43
,
44
,
45
,
46
,
47
,
48
,
49
,
50
,
51
,
52
,
53
,
54
,
55
,
56
,
57
,
58
,
59
,
60
,
61
,
62
,
63
,
64
,
65
,
66
,
67
,
68
,
69
,
70
,
71
,
72
,
73
,
74
,
75
,
76
,
77
,
78
,
79
,
80
,
81
,
82
,
83
,
84
,
85
,
86
,
87
,
88
,
89
}
See also 90 in Linked Open Numbers
(back to √2)