# data[].attributes.body
is the set of elements that do not belong to a set of reference.  Given two sets A and B, where B is a subset of A, the set of B than A is the set difference A-B (difference sets).

# data[].attributes.body
Define Cartesian product AxB of two sets A and B the set of all an element of A and as a second element an element of B ordered pairs whose first element
Data sets
A = { 1, 2, 3, 4 }
B = { a, b, c }
I build all couples considering as the first item in an element of A and as a second element an element of B
Axb= { (1,a) (1,b) (1,c) (2,a) (2,b) (2,c) (3,a) (3,b) (3,c) (4,a) (4,b) (4,c) }

# data[].attributes.body
is CARTESIAN PRODUCT

# data[].attributes.body
the main property of the Union and intersection are:
ASSOCIATIVE PROPRETY
for union:      (A  B)  C = A  (B  C)
for intersection :      (A  B)  C = A  (B  C)

PROPERTY OF THE EMPTY SET
for union:      A  Ø = Ø  A = A

for union  the empty set is the neutral element

for intersection:      A  Ø = Ø  A = Ø
to the intersection of the empty set is the absorbing element
DISTRIBUTIVE PROPERITY
the Union compared to the intersection:
A  (B  C) = (A  B)  (A  C)
the intersection compared to the Union:
A  (B  C) = (A  B)  (A  C)

# data[].attributes.body
You define the difference between two sets all elements of the first set that do not belong to the second set;

# data[].attributes.body
x ∈ A∪B ⇔ x ∈ A x ∈

# data[].attributes.body
x ∈ A∩B ⇔ x ∈ A e x ∈
when both A and B belongs is intersection
C∩D=∅=disjoint

# data[].attributes.body
B⊆A ⇔ ∄x∈A,x∈B
↓
There is an element of A what is an element of B
∅⊆A=A=∅

# data[].attributes.body
Proper subset:
B⊂A ⇔ Every element of B is also an element of A
↓

# data[].attributes.body
a set is a well defined collection of distinct object i.e. the nature of the nature of the object is the same or in other words the object in a set may be anything:numbers,people,places,letters,etc.
These objects are called the elements or membres of the set.

# data[].attributes.body
The signs are:
icates a collection
A=indefined
a=indicates an element of A
∈=belongs
∉=doesen't belongs
∅=empty set

The sets must be well dA=indefined
EXAMPLE:
A={a,b,c} TABULOR FORM