Thank you for your letters!
As I wrote, I'm interested to greatly expand my graph of mathematical areas:
So I need to take a database approach of sorts.
I'm realizing that there are a couple of obstacles working with Neo4j. http://neo4j.com
It's basically a powerful backend, I think.
A possible front end for Neo4j would be Linkurious https://linkurio.us That costs 1,000 euros.
TheBrain http://www.thebrain.com has a free version which is quite robust. I could edit with that. But if I wanted to export, then I would have to pay about $200 for the Pro version. I might afford that but I'm wondering if other options might not be better.
Really, in terms of creating nodes and links, the most nimble solution might be to create database tables and forms. That might actually be most ergonomic. Then I would export the database information and import it into a graph data visualization tool. If I was using Microsoft Access on Windows then I would take this approach. However, I have found OpenOffice Base on Linux to be quite flawed, ever crashing and losing data. I wonder if Kexi is better http://www.kexi-project.org
Is there any open source graph data visualization tool that you or others might recommend? I see https://gephi.org and http://www.yworks.com I think I like the latter: https://www.yworks.com/actions/imageviewer.php?img=aceprv7.928a4430.graphml&album=ygucd&fs=1