The Gateway to Computer Science Excellence
+18 votes

Which one of the following is NOT necessarily a property of a Group?

  1. Commutativity
  2. Associativity   
  3. Existence of inverse for every element   
  4. Existence of identity
in Set Theory & Algebra by Boss (17.5k points)
edited by | 1.4k views

3 Answers

+25 votes
Best answer
  • Groupoid: closure property.
  • Semigroup: closure, associative.
  • Monoid-closure: associative, identity.
  • Group: closure, associative, identity, inverse.
  • Abelian group: group properties + commutativity 

So, ans should be A.

by Active (2.4k points)
edited by

A groupoid can be seen as a Group with a partial function replacing the binary operation.

Groupoid satisfies all properties of group not only closure property.


+9 votes

(A) Commutativity is a property of Abelian group

Rest 3 and closure property is needed for a group.

by Active (2.4k points)
+3 votes

A group is a setG, together with an operation • (called the group law of G) that combines any two elements a and b to form another element, denoted a • b or ab. To qualify as a group, the set and operation, (G, •), must satisfy four requirements known as the group axioms


For all ab in G, the result of the operation, a • b, is also in G.


For all ab and c in G, (a • b) • c = a • (b • c).

Identity element

There exists an element e in G such that, for every element a in G, the equation e • a = a • e = a holds. Such an element is unique, and thus one speaks of theidentity element.

Inverse element

For each a in G, there exists an element b in G, commonly denoted a−1 (or −a, if the operation is denoted "+"), such that a • b = b • a = e, where e is the identity element.

The result of an operation may depend on the order of the operands. In other words, the result of combining element a with element b need not yield the same result as combining element b with element a; the equation

a • b = b • 

Abelian Group

   An abelian group is a setA, together with an operation • that combines any two elements a and to form another element denoted a • b. The symbol • is a general placeholder for a concretely given operation. To qualify as an abelian group, the set and operation, (A, •), must satisfy five requirements known as the abelian group axioms:


For all ab in A, the result of the operation a • b is also in A.


For all ab and c in A, the equation (a • b) • c = a • (b • c) holds.

Identity element

There exists an element e in A, such that for all elements a in A, the equation e • a = a • e = aholds.

Inverse element

For each a in A, there exists an element b in A such that a • b = b • a = e, where e is the identity element.


For all ab in Aa • b = b • a.

A group in which the group operation is not commutative is called a "non-abelian group" or "non-commutative group"

by Active (4.2k points)
wat is magma in the pic ???
magma is groupoid mam

Related questions

Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true
50,737 questions
57,306 answers
105,014 users