Element may not have 2-sided inverse in infinite ring
17059
A ring element with a left inverse but no right inverse?
75970
$\mathbb Z[1/2]$ is not finitely generated?
52081
Why is not the ring $\mathbb{Z}[2\sqrt{2}]$ a unique factorization domain?
112485
Allowing the zero element in a field to have an inverse
46698
Showing a set is closed under inverses
87382
Non-invertible elements form an ideal
14343
Every nonzero element in a finite ring is either a unit or a zero divisor
24351
The ring $\Bbb Z\left [\frac{-1+\sqrt{-19}}{2}\right ]$ is not a Euclidean domain
21229
If an element is not in the set difference $A\setminus B \: \:?$
66451
In a ring, how do we prove that a * 0 = 0?
88474
$\mathbb{A}^{2}$ not isomorphic to affine space minus the origin
48009
Left inverse implies right inverse in a finite ring
39788
$a+1,a-1$ invertible for nilpotent element
7536
Is there an idempotent element in a finite semigroup?
141100
Nontrivial subring with unity different from the whole ring?
18066
Prove that any non-zero-divisor of a finite dimensional algebra has an inverse
1577
Order of nontrivial elements is 2 implies Abelian group