Skip to main content
Search type Search syntax
Tags [tag]
Exact "words here"
Author user:1234
user:me (yours)
Score score:3 (3+)
score:0 (none)
Answers answers:3 (3+)
answers:0 (none)
isaccepted:yes
hasaccepted:no
inquestion:1234
Views views:250
Code code:"if (foo != bar)"
Sections title:apples
body:"apples oranges"
URL url:"*.example.com"
Saves in:saves
Status closed:yes
duplicate:no
migrated:no
wiki:no
Types is:question
is:answer
Exclude -[tag]
-apples
For more details on advanced search visit our help page
Results tagged with
Search options answers only not deleted user 9269

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.

10 votes

Paris-Harrington via overspill?

This edit includes a fleshed-out version of Smorynski's remark about taking advantage of a nonstandard model of arithmetic (instead of König's lemma) to prove the Paris-Harrington (PH) principle from …
Ali Enayat's user avatar
  • 17.7k
7 votes

dense orders are saturated

Philip Ehrich and Emil Jeřábek have given useful references (and Dave Marker and I seem to have simultaneously written our responses). This note is to point out that the result itself was original …
Ali Enayat's user avatar
  • 17.7k
18 votes
Accepted

SPOT as a conservative extension of Zermelo–Fraenkel

In plain terms, the conservativity of SPOT over ZF means that if a particular statement S in the language of ZF is provable in SPOT, then ZF can already prove S (with a possibly different proof). Note …
Ali Enayat's user avatar
  • 17.7k
11 votes

Automorphisms of the hyperreals over the rationals and nontrivial automorphism groups

This note complement Joel's, who pointed out that every first order theory with an infinite model has a model with many automorphisms (this was first proved by Ehrenfeucht and Mostowski in their famou …
Ali Enayat's user avatar
  • 17.7k
12 votes

What is the spectrum of possible cofinality types for cuts in an ordered field? Or in a mode...

The theorem below answers question 4, and the corollary answers question 3. See also Theorem 2. Theorem 1. For every pair of infinite cardinals $(\kappa$,$\lambda)$, there is a model $M$ of $PA$ …
Ali Enayat's user avatar
  • 17.7k