Is a Cancellative Semigroup the Same as a Group?

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In summary, the conversation discusses the requirements for a set to be considered a group with respect to an operation. It is mentioned that the set must be closed, associative, and fulfill both cancellation laws. However, it is noted that this may not always result in a group, as seen in the example of the set of positive integers under multiplication.
  • #1
prashantgolu
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if a set is closed and associative with respect to an operation * and both cancllation laws hold...prove that the set is a group wrt *.
 
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  • #2
Is this homework? Have you made an attempt at the problem? Show us what you have.
 
  • #3
thnx..this one is done...
 
  • #4
It looks to me like you are trying to prove something that is NOT TRUE. For example, the set of positive integers is closed under ordinary mulitplication which is associative and both cancellation laws hold. But this is not a group.
 
  • #5
Ah, indeed. And if you take the integers ≥ 2 under multiplication, then you don't even get a monoid. Apparently such a thing is called a cancellative semigroup.
 

FAQ: Is a Cancellative Semigroup the Same as a Group?

What are cancellation laws in group theory?

Cancellation laws in group theory state that if two elements in a group have the same result after a group operation, then they are equal. In other words, if a * b = a * c, then b = c. This property allows for simplification of equations and easier manipulation of group elements.

How are cancellation laws applied in real life situations?

Cancellation laws are often used in various fields of science and mathematics, such as physics, chemistry, and cryptography. For example, in physics, they can be used to simplify equations and solve for unknown variables. In cryptography, they are used to ensure the security of encrypted messages.

What is the difference between left and right cancellation laws?

The left cancellation law states that if a * b = a * c, then b = c, while the right cancellation law states that if b * a = c * a, then b = c. Essentially, the left cancellation law applies when the element to the left of the group operation is the same, while the right cancellation law applies when the element to the right of the group operation is the same.

Are cancellation laws always applicable in group theory?

No, cancellation laws only apply in groups that are closed under the group operation. This means that the result of the operation must also be an element of the group. If the group is not closed, then cancellation laws may not hold.

Can cancellation laws be applied to non-commutative groups?

Yes, cancellation laws can be applied to non-commutative groups, as long as the group is closed under the group operation. However, the order of the elements may affect the result, so the left and right cancellation laws may not be equivalent in this case.

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