What is an example of a non standard model of Peano Arithmetic?
52429
Explicit countable elementary extension of $\mathbb{N}$
59679
How is exponentiation defined in Peano arithmetic?
158924
Example of composition of two normal field extensions which is not normal.
50602
Does uncountable summation, with a finite sum, ever occur in mathematics?
87580
Canonical examples of inner product spaces that are not Hilbert spaces?
10943
What is an example of a radical of sum of ideals not being equal to the sum of radicals?
36626
Multiplication cancellation property by Peano axioms
154961
Are there simple models of Euclid's postulates that violate Pasch's theorem or Pasch's axiom?
66679
What are the models of quantum computation?
29084
Largest integer that can't be represented as a non-negative linear combination of $m, n = mn - m - n$? Why?
101095
Constructing an example s.t. $\operatorname{Hom}_R(M,N)$ is not finitely generated
106716
The sum of square roots of non-perfect squares is never integer
61084
Examples of non-isomorphic fields with isomorphic group of units and additive group structure
86724
Example of a non-zero module that has no associated primes
76597
Examples of provably${}^n$ unprovable statements
18465
Sum and product of two transcendental numbers can't be both algebraic
7010
Example of two non-isomorphic fields which embed inside each other