# equivalence relation in discrete mathematics

Equivalence Relations (a) (5) Prove that the following is an equivalence relation. Forums Login. Since $$xRa, x \in[a],$$ by definition of equivalence classes. if $$R$$ is an equivalence relation on any non-empty set $$A$$, then the distinct set of equivalence classes of $$R$$ forms a partition of $$A$$. Equivalence relations Peter Mayr CU, Discrete Math, April 3, 2020. Define the relation $$\sim$$ on $$\mathbb{Q}$$ by $x\sim y \,\Leftrightarrow\, 2(x-y)\in\mathbb{Z}.$  $$\sim$$ is an equivalence relation. Since $$y \in A_i \wedge x \in A_i, \qquad yRx.$$ Notice that $\mathbb{R}^+ = \bigcup_{x\in(0,1]} [x],$ which means that the equivalence classes $$[x]$$, where $$x\in(0,1]$$, form a partition of $$\mathbb{R}$$. Equivalence Relations. A relation $$R$$ on a set $$A$$ is an equivalence relation if it is reflexive, symmetric, and transitive. then R is an equivalence relation, and the distinct equivalence classes of R form the original partition {A 1, ,A n}.. Equivalence relations Peter Mayr CU, Discrete Math, April 3, 2020. Chemistry Help. The equivalence relation has the properties: An equivalence class is defined as a subset of the form, where is an element of and the notation " " is used to mean that there is an equivalence relation between and. If $$R$$ is an equivalence relation on the set $$A$$, its equivalence classes form a partition of $$A$$. Home Course Notes Exercises Mock Exam About. If is reflexive, symmetric, and transitive then it is said to be a equivalence relation. Exercise $$\PageIndex{9}\label{ex:equivrel-09}$$. A relation that is all three of reflexive, symmetric, and transitive, is called an equivalence relation. Now WMST $$\{A_1, A_2,A_3, ...\}$$ is pairwise disjoint. (Beware: some authors do not use the term codomain(range), and use the term range inst… \end{array}\] It is clear that every integer belongs to exactly one of these four sets. Given $$P=\{A_1,A_2,A_3,...\}$$ is a partition of set $$A$$, the relation, $$R$$,  induced by the partition, $$P$$, is defined as follows: $\mbox{ For all }x,y \in A, xRy \leftrightarrow \exists A_i \in P (x \in A_i \wedge y \in A_i).$, Consider set $$S=\{a,b,c,d\}$$ with this partition: $$\big \{ \{a,b\},\{c\},\{d\} \big\}.$$. In each equivalence class, all the elements are related and every element in $$A$$ belongs to one and only one equivalence class. Forums. Legal. of elements of , satisfying certain properties. A relation on a set A is an equivalence relation if it is reflexive, symmetric, and transitive. We intuitively know what it means to be "equivalent", and some relations satisfy these intuitions, while others do not. $$\exists i (x \in A_i).$$  Since $$x \in A_i \wedge x \in A_i,$$ $$xRx$$ by the definition of a relation induced by a partition. Relation R is Symmetric, i.e., aRb bRa; Relation R is transitive, i.e., aRb and bRc aRc. Define $$\sim$$ on $$\mathbb{R}^+$$ according to $x\sim y \,\Leftrightarrow\, x-y\in\mathbb{Z}.$ Hence, two positive real numbers are related if and only if they have the same decimal parts. Define three equivalence relations on the set of students in your discrete mathematics class different from the relations discussed in the text. If the relation R is reflexive, symmetric and transitive for a set, then it is called an equivalence relation. 1st - 5th grade . These are the only possible cases. In other words, $$S\sim X$$ if $$S$$ contains the same element in $$X\cap T$$, plus possibly some elements not in $$T$$. Let $$x \in [a], \mbox{ then }xRa$$ by definition of equivalence class. $$\exists x (x \in [a] \wedge x \in [b])$$ by definition of empty set & intersection. Combinatorial algebra: permutations, combinations, sums of finite sequences. By the definition of equivalence class, $$x \in A$$. Click here to get the proofs and solved examples. For an equivalence relation, due to transitivity and symmetry, all the elements related to a fixed element must be related to each other. https://mathworld.wolfram.com/EquivalenceRelation.html. Save. Factorial superfactorials hyperfactorial primalial . Proof: The equivalence classes split A into disjoint subsets. Exercise $$\PageIndex{2}\label{ex:equivrel-02}$$. From the equivalence class $$\{2,4,5,6\}$$, any pair of elements produce an ordered pair that belongs to $$R$$. The overall idea in this section is that given an equivalence relation on set $$A$$, the collection of equivalence classes forms a partition of set $$A,$$ (Theorem 6.3.3). Combinatorics. Equivalence Relations. Discrete Mathematics Binary Operation with introduction, sets theory, types of sets, set operations, algebra of sets, multisets, induction, relations, functions and algorithms etc. Consider the following relation on $$\{a,b,c,d,e\}$$: $\displaylines{ R = \{(a,a),(a,c),(a,e),(b,b),(b,d),(c,a),(c,c),(c,e), \cr (d,b),(d,d),(e,a),(e,c),(e,e)\}. Exercise $$\PageIndex{8}\label{ex:equivrel-08}$$. Answers > Math > Discrete Mathematics . a. f(0;0);(1;1);(2;2);(3;3)g. It is an equivalence relation. The equivalence relation is a rigorous mathematical definition of such ordinary notions as “sameness” or “indistinguishability”. Define the relation $$\sim$$ on $$\mathbb{Q}$$ by \[x\sim y \,\Leftrightarrow\, \frac{x-y}{2}\in\mathbb{Z}.$ Show that $$\sim$$ is an equivalence relation. An equivalence class can be represented by any element in that equivalence class. It is obvious that $$\mathbb{Z}^*=[1]\cup[-1]$$. b) find the equivalence classes for $$\sim$$. Exercise $$\PageIndex{4}\label{ex:equivrel-04}$$. Theorem 6.3.3 and Theorem 6.3.4 together are known as the Fundamental Theorem on Equivalence Relations. Case 1: $$[a] \cap [b]= \emptyset$$ Example – Show that the relation is an equivalence relation. All the integers having the same remainder when divided by 4 are related to each other. $$\therefore [a]=[b]$$ by the definition of set equality. One may regard equivalence classes as objects with many aliases. 2 months ago. For instance, $$[3]=\{3\}$$, $$[2]=\{2,4\}$$, $$[1]=\{1,5\}$$, and $$[-5]=\{-5,11\}$$. WMST $$A_1 \cup A_2 \cup A_3 \cup ...=A.$$ Lemma Let A be a set and R an equivalence relation on A. a. f(0;0);(1;1);(2;2);(3;3)g. It is an equivalence relation. 1st - 5th grade. Since $$a R b$$, we also have $$b R a,$$ by symmetry. So, in Example 6.3.2, $$[S_2] =[S_3]=[S_1] =\{S_1,S_2,S_3\}.$$  This equality of equivalence classes will be formalized in Lemma 6.3.1. Discrete Mathematics Online Lecture Notes via Web. $$[2] = \{...,-10,-6,-2,2,6,10,14,...\}$$ So, if $$a,b \in A$$ then either $$[a] \cap [b]= \emptyset$$ or $$[a]=[b].$$. $$[0] = \{...,-12,-8,-4,0,4,8,12,...\}$$ We give examples and then prove a connection between equivalence relations and partitions of a set. The element in the brackets, [  ]  is called the representative of the equivalence class. In this case $$[a] \cap [b]= \emptyset$$  or  $$[a]=[b]$$ is true. Discrete Mathematics by Section 6.5 and Its Applications 4/E Kenneth Rosen TP 1 Section 6.5 Equivalence Relations Now we group properties of relations together to define new types of important relations. Greek philosopher, Aristotle, was the pioneer of … what is equivalence relation Preview this quiz on Quizizz. Let $$\mathbb{Z}^*$$ be the set of nonzero integers. Select all the correct options below ... From the options, I noted that all the relations are connected to the equivalence relation. of , and we say " is related to ," then the properties are. MA: Addison-Wesley, p. 18, 1990. Example 6.3.12. Let $$R$$ be an equivalence relation on set $$A$$. Discrete Math: Apr 17, 2015: Equivalence relations and partitions. Let $$x \in A.$$ Since the union of the sets in the partition $$P=A,$$ $$x$$ must belong to at least one set in $$P.$$ Also, when we specify just one set, such as a ∼ b is a relation on set B, that means the domain & codomain are both set B. Characteristics of equivalence relations . $$[1] = \{...,-11,-7,-3,1,5,9,13,...\}$$ From MathWorld--A Wolfram Web Resource. Over $$\mathbb{Z}^*$$, define $R_3 = \{ (m,n) \mid m,n\in\mathbb{Z}^* \mbox{ and } mn > 0\}.$ It is not difficult to verify that $$R_3$$ is an equivalence relation. Unlimited random practice problems and answers with built-in Step-by-step solutions. Thus $$x \in [x]$$. Grishin (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. Edit. 86 times. If $$R$$ is an equivalence relation on any non-empty set $$A$$, then the distinct set of equivalence classes of $$R$$ forms a partition of $$A$$. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Knowledge-based programming for everyone. 5 CS 441 Discrete mathematics for CS M. Hauskrecht Equivalence classes and partitions Theorem: Let R be an equivalence relation on a set A.Then the union of all the equivalence classes of R is A: Proof: an element a of A is in its own equivalence class [a]R so union cover A. Theorem: The equivalence classes form a partition of A. Math 114 Discrete Mathematics Section 8.5, selected answers D Joyce, Spring 2018 1. I was studying but realized that I am having trouble grasping the representations of relations using Zero One Matrices. Relation and Function-Discrete Math DRAFT. Reflexive Since $$aRb$$, $$[a]=[b]$$ by Lemma 6.3.1. Relation and Function-Discrete Math DRAFT. Skiena, S. Implementing Discrete Mathematics: Combinatorics and Graph Theory with Mathematica. Example $$\PageIndex{3}\label{eg:sameLN}$$. If $$R$$ is an equivalence relation on the set $$A$$, its equivalence classes form a partition of $$A$$. Relations, equivalence relations, and partitions; relational composition & converse, transitive closure; orders, least upper and greatest lower bounds. Determine the equivalence classes for each of these equivalence relations. Discrete Mathematics. Determine the equivalence classes for … Proof: Note ka+ bik= ka+ bikso a+ bi is related to itself. In mathematics, an equivalence relation is a binary relation that is reflexive, symmetric and transitive. Two complex numbers, a + bi and c + di, are related if ka+ bik= kc+ dik: Note ka+ bik= p a2 + b2: The relation is re exive. Take a closer look at Example 6.3.1. Suppose $$R$$ is an equivalence relation on any non-empty set $$A$$. We have shown if $$x \in[b] \mbox{ then } x \in [a]$$, thus  $$[b] \subseteq [a],$$ by definition of subset. The equivalence relation A in the set M means that... Equivalence relation . https://mathworld.wolfram.com/EquivalenceRelation.html, Motion Traced on the Torus and From this we see that $$\{[0], [1], [2], [3]\}$$ is a partition of $$\mathbb{Z}$$. Equivalent Fractions. Have questions or comments? Exercise $$\PageIndex{10}\label{ex:equivrel-10}$$. The course exercises are meant for the students of the course of Discrete Mathematics and Logic at the Free University of Bozen ... that R is an equivalence relation. Glossary of graph theory . Denoted by X ~ Y. Denote the equivalence classes as $$A_1, A_2,A_3, ...$$. $$xRa$$ and $$xRb$$ by definition of equivalence classes. View hw2.pdf from CSE -173 at North South University. For this relation $$\sim$$ on $$\mathbb{Z}$$ defined by $$m\sim n \,\Leftrightarrow\, 3\mid(m+2n)$$: a) show $$\sim$$ is an equivalence relation. Each part below gives a partition of $$A=\{a,b,c,d,e,f,g\}$$. }\) In fact, the term equivalence relation is used because those relations which satisfy the definition behave quite like the equality relation. This relation turns out to be an equivalence relation, with each component forming an equivalence class. A primitive root of a prime p is an integer r such that every integer not divisible by p is congruent to a power of r modulo p. If r is a primitive root of p and re ≡ a (mod p), then e is the discrete logarithm of a modulo p to the base r. Finding discrete logarithms turns … We have $$aRx$$ and $$xRb$$, so $$aRb$$ by transitivity. This article was adapted from an original article by V.N. A relation $$r$$ on a set $$A$$ is called an equivalence relation if and only if it is reflexive, symmetric, and transitive. Algebra Pre-Calculus Geometry Trigonometry Calculus Advanced Algebra Discrete Math Differential Geometry Differential Equations Number Theory Statistics & Probability Business Math Challenge Problems Math Software. The possible remainders are 0, 1, 2, 3. CSE 173: Discrete Mathematics Homework 2: Relation Due on Thursday: 23-07-2020 (class time) Submission: Only handwritten sheets (scan answer where these three properties are completely independent. (a) Every element in set $$A$$ is related to every other element in set $$A.$$. However, the rigorous treatment of sets happened only in the 19-th century due to the German math-ematician Georg Cantor. In mathematics, when the elements of some set S have a notion of equivalence (formalized as an equivalence relation) defined on them, then one may naturally split the set S into equivalence classes. $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$, 6.3: Equivalence Relations and Partitions, [ "article:topic", "authorname:hkwong", "license:ccbyncsa", "showtoc:yes", "equivalence relation", "Fundamental Theorem on Equivalence Relation" ], $$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$ $$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\kernel}{\mathrm{null}\,}$$ $$\newcommand{\range}{\mathrm{range}\,}$$ $$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$ $$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$ $$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$ $$\newcommand{\Span}{\mathrm{span}}$$, $a\sim b \,\Leftrightarrow\, a \mbox{ mod } 4 = b \mbox{ mod } 4.$, $a\sim b \,\Leftrightarrow\, a \mbox{ mod } 3 = b \mbox{ mod } 3.$, $S_i \sim S_j\,\Leftrightarrow\, |S_i|=|S_j|.$, $\begin{array}{lclcr} {[0]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 0 \} &=& 4\mathbb{Z}, \\ {[1]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 1 \} &=& 1+4\mathbb{Z}, \\ {[2]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 2 \} &=& 2+4\mathbb{Z}, \\ {[3]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 3 \} &=& 3+4\mathbb{Z}. thus $$xRb$$ by transitivity (since $$R$$ is an equivalence relation). Two sets will be related by $$\sim$$ if they have the same number of elements. I'm keeping it in mind, but the options are all divided into different relations. In particular, let $$S=\{1,2,3,4,5\}$$ and $$T=\{1,3\}$$. Set theory is the foundation of mathematics. \hskip0.7in \cr}$ This is an equivalence relation. Let $$A$$ be a set with partition $$P=\{A_1,A_2,A_3,...\}$$ and $$R$$ be a relation induced by partition $$P.$$  WMST $$R$$ is an equivalence relation. Weisstein, Eric W. "Equivalence Relation." We have demonstrated both conditions for a collection of sets to be a partition and we can conclude  … Define a relation $$\sim$$ on $$\mathbb{Z}$$ by $a\sim b \,\Leftrightarrow\, a \mbox{ mod } 3 = b \mbox{ mod } 3.$ Find the equivalence classes of $$\sim$$. 2 The relation is symmetric. An equivalence relation on a set X is a subset of X×X, i.e., a collection R of ordered pairs of elements of X, satisfying certain properties. sirjheg. Consequently, two elements and related by an equivalence relation are said to be equivalent. (d) Every element in set $$A$$ is related to itself. They essentially assert some kind of equality notion, or equivalence, hence the name. Write "xRy" to mean (x,y) is an element of R, and we say "x is related to y," then the properties are 1. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. COMPSCI 230: Discrete Mathematics for Computer Science February 11, 2019 Lecture 9 Lecturer: Debmalya Panigrahi Scribe: Kevin Sun 1 Overview In this lecture, we study a special class of relations on a set known as equivalence relations. $$[S_2] = \{S_1,S_2,S_3\}$$ So, $$A \subseteq A_1 \cup A_2 \cup A_3 \cup ...$$ by definition of subset. Example $$\PageIndex{7}\label{eg:equivrelat-10}$$. To show a relation is notan equivalence relation, show it does not satisfy at least one of these properties. Graph theory. Learn the core topics of Discrete Math to open doors to Computer Science, Data Science, Actuarial Science, and more! Conversely, given a partition $$\cal P$$, we could define a relation that relates all members in the same component. Determine the contents of its equivalence classes. Next we show $$A \subseteq A_1 \cup A_2 \cup A_3 \cup ...$$. Stewart, I. and Tall, D. The The relation "is equal to" is the canonical example of an equivalence relation, where for any objects a, b, and c: In fact, it’s equality, the best equivalence relation. The relation $$R$$ determines the membership in each equivalence class, and every element in the equivalence class can be used to represent that equivalence class. It can be shown that any two equivalence classes are either equal or disjoint, hence the collection of equivalence classes forms a … In other words, the equivalence classes are the straight lines of the form $$y=x+k$$ for some constant $$k$$. $$[x]=A_i,$$ for some $$i$$ since $$[x]$$ is an equivalence class of $$R$$. $$\exists i (x \in A_i \wedge y \in A_i)$$ and $$\exists j (y \in A_j \wedge z \in A_j)$$ by the definition of a relation induced by a partition. $$\therefore R$$ is symmetric. If S is a set with an equivalence relation R, then it is easy to see that the equivalence classes of R form a partition of the set S. More interesting is the fact that the converse of this statement is true. Prove that the relation $$\sim$$ in Example 6.3.4 is indeed an equivalence relation. › Discrete Math. Since $$y$$ belongs to both these sets, $$A_i \cap A_j \neq \emptyset,$$ thus $$A_i = A_j.$$  $$\therefore R$$ is transitive. Thus, if we know one element in the group, we essentially know all its “relatives.”. Physics Help. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Edit. Exercises for Discrete Maths Discrete Maths Teacher: Alessandro Artale ... Science Free University of Bozen-Bolzano Disclaimer. Determine the properties of an equivalence relation that the others lack. First we will show $$[a] \subseteq [b].$$ (b) There are two equivalence classes: $$[0]=\mbox{ the set of even integers }$$,  and $$[1]=\mbox{ the set of odd integers }$$. R must be: Because the sets in a partition are pairwise disjoint, either $$A_i = A_j$$ or $$A_i \cap A_j = \emptyset.$$ (a) Write the equivalence classes for this equivalence relation. A relation in mathematics defines the relationship between two different sets of information. https://www.tutorialspoint.com/.../discrete_mathematics_relations.htm Let $$S= \mathscr{P}(\{1,2,3\})=\big \{ \emptyset, \{1\},\{2\},\{3\},\{1,2\},\{1,3\},\{2,3\},\{1,2,3\} \big \}.$$, $$S_0=\emptyset, \qquad S_1=\{1\}, \qquad S_2=\{2\}, \qquad S_3=\{3\}, \qquad S_4=\{1,2\},\qquad S_5=\{1,3\},\qquad S_6=\{2,3\},\qquad S_7=\{1,2,3\}.$$, Define this equivalence relation $$\sim$$ on $$S$$ by $S_i \sim S_j\,\Leftrightarrow\, |S_i|=|S_j|.$. We have shown $$R$$ is reflexive, symmetric and transitive, so $$R$$ is an equivalence relation on set $$A.$$ Now we have $$x R b\mbox{ and } bRa,$$ thus $$xRa$$ by transitivity. Discrete Math. If $$R$$ is an equivalence relation on $$A$$, then $$a R b \rightarrow [a]=[b]$$. Reflexive: for all, Hints help you try the next step on your own. The equivalence classes are the sets $\begin{array}{lclcr} {[0]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 0 \} &=& 4\mathbb{Z}, \\ {[1]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 1 \} &=& 1+4\mathbb{Z}, \\ {[2]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 2 \} &=& 2+4\mathbb{Z}, \\ {[3]} &=& \{n\in\mathbb{Z} \mid n\bmod 4 = 3 \} &=& 3+4\mathbb{Z}. A relation R on a set A is called an equivalence relation if it satisfies following three properties: Relation R is Reflexive, i.e. Explore anything with the first computational knowledge engine. Which of these relations on the set f0;1;2;3g are equivalence relations? Menu Exploring equivalence relation on a set. And so, $$A_1 \cup A_2 \cup A_3 \cup ...=A,$$ by the definition of equality of sets. He was solely responsible in ensuring that sets had a home in mathematics. of , i.e., a collection of ordered pairs Foundations of Mathematics. Hence, \[\mathbb{Z} = [0] \cup [1] \cup [2] \cup [3].$ These four sets are pairwise disjoint. 3. In Matrix form, if a 12 is present in relation, then a 21 is also present in relation and As we know reflexive relation is part of symmetric relation. a) True or false: $$\{1,2,4\}\sim\{1,4,5\}$$? So we have to take extra care when we deal with equivalence classes. Computer siences mathematics Psychology ... Discrete Math. Exam 2: Equivalence, Partial Orders, Counts 2 2. An equivalence class is defined as a subset of the form {x in X:xRa}, where a is an element of X and the notation "xRy" is used to mean that there is an equivalence relation between x and y. Describe its equivalence classes. It can be shown that any two equivalence classes are either equal or disjoint, hence the collection of equivalence classes forms a partition of X. Basic building block for types of objects in discrete mathematics. Write " " to mean is an element of, and we say " is related to," then the properties are 1. 2 Equivalence Relations Deﬁnition 1. (b) Write the equivalence relation as a set of ordered pairs. Recall De nition A relation R A A is an equivalence on A if R is 1.re exive, 8x 2A: xRx 2.symmetric, 8x;y 2A: xRy )yRx 3.transitive. Discrete Mathematics Binary Operation with introduction, sets theory, types of sets, set operations, algebra of sets, multisets, induction, relations, functions and algorithms etc. Congruence Modulo is an Equivalence Relation Convince yourself that the slices used in the previous example have the following properties: Every pair of values in a slice are related to each other We will never find a value in more than one slice (slices are mutually disjoint) Zermelo-Fraenkel set theory (ZF) is standard. If two sets are considered, the relation between them will be established if there is a connection between the elements of two or more non-empty sets.