Subsets of Natural Numbers are Countable

Androma

Home

Return to the main page

Pages

Browse all wiki pages

Theorems

Mathematical theorems & proofs

Notation

Symbol & convention glossary

Areas of Mathematics

Explore mathematical fields

Discussions

Community conversations

Quick Links

Study TeX Projects Learn Events Papers Advanced Search Documentation Review Queue Blog Notes Organizations Research Groups

Subsets of Natural Numbers are Countable

Feedback
Sign in Register

Sign in to Androma

We’ll send a one-time code to your email — no passwords, ever.

Continue with Google Continue with ORCID

or with email

Email address

Passwordless. Each sign-in is verified by a 6-digit code.

Check your inbox

We sent a 6-digit code to . Enter it below to continue.

–

Didn’t get it? ·

One last step

Tell us how you’d like to appear on Androma. You can change your name later, but your handle is permanent.

Your name

Shown on your profile and next to every page or theorem you contribute.

Handle

androma.org/u/

3–20 characters. Letters, numbers, hyphens, underscores. Cannot be changed.

I agree to the Terms of Service and Privacy Policy, and that my contributions will be licensed under CC BY-SA 4.0.

Androma

Quick setup

What brings you to Androma?

Pick the closest answer and we will show the parts of the platform most likely to matter first. You can use everything either way.

Learning math

Recommended start

Start with a route through the knowledge graph.

Androma connects pages, theorems, notes, and practice so the next useful thing is never far away.

Start with this Show me everything

This only chooses your first stop. Androma does not lock features by role, and you can come back to any area whenever you like.

Live shape of the platform

Search: compactness in metric spaces

Heine-Borel Theorem

A theorem page links definitions, prerequisites, proofs, and nearby ideas into one navigable object.

1Find a page or theorem

2Follow the prerequisite trail

3Save it to study

4Discuss or contribute

A wiki that behaves like a workspace.

Read, write, teach, discuss, and revise around the same mathematical objects instead of scattering context across separate tools.

Subsets of Natural Numbers are Countable Issues

Issues

New issue

Issues Pull Requests

No open issues

There are no open issues for this theorem yet.

New issue

Explore

All Pages
Theorems
Math Areas
Study
Search

Create

New Page
New Theorem
Papers

Community

Discussions
Research Groups
Events

Resources

Project Status
Documentation
GitHub

More ways to explore: Browse all pages or explore by area.

Home Messages Schedule Study Profile