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Nonstandard analysis is a way of doing calculus and analysis with infinitesimals. The historical approach of Leibniz, Euler, and others to infinitesimal calculus was gradually replaced by epsilon, delta techniques in the context of a real continuum, in the 19th century. It was not until the 1960s that Abraham Robinson developed a theory of a hyperreal continuum that allows for a development of analysis procedurally akin to that of its founders.

9 votes
2 answers
473 views

Hyperreal finitely-additive measure on [0,1) assigning $b-a$ to $[a,b)$ or $(a,b]$ and infin...

Is there a hyperreal-valued finitely additive measure on all the subsets of [0,1), or at least the Borel ones, that assigns $b-a$ to $[a,b)$ and to $(a,b]$ for all $a\lt b,$ and assigns an infinit …
Alexander Pruss's user avatar
4 votes
0 answers
145 views

Self homomorphisms of hyperreals fixing the reals

What do we know about the circumstances (whether having to do with the axioms of set theory or the model itself) under which a field $F$ of hyperreals (=ultrapower of $\mathbb R$ with respect to a non …
Alexander Pruss's user avatar
3 votes
2 answers
294 views

Hyperfinite set containing the reals, with specified upper bound on internal cardinality?

Is this true? For any hyperfinite $n$ that isn't finite, there is a hyperfinite set $A$ such that $\mathbb R \subset A$ and $|A|\le n$ (that's the crucial part, of course)? Intuitively it seems righ …
Alexander Pruss's user avatar
3 votes
1 answer
319 views

A stronger version of supramenability?

A group $G$ is supramenable iff for all $\varnothing\ne A\subseteq G$ there is a finitely-additive left-$G$-invariant measure $\mu_A$ on $G$ with $\mu_A(A)=1$. I'm interested in a seemingly stronger …
Alexander Pruss's user avatar