@modulux The REPL's include an input method that allows you to type them using a prefix character (usually backquote). So to type ⊂ you press backquote followed by z.

The web-based client shows the keyboard layout: kapdemo.dhsdevelopments.com/cl…

There's also an Emacs mode for people who prefer that. It's also my intent to create a custom keyboard layout for Linux, but I haven't done that because I personally have no need for it. There is one for APL though, which has almost all the symbols needed.