Okay I've gone and broke it and I have no idea why; the addSupporting function is now no longer woring; adding anything other than an Axiom causes it to break when you switch selections on the left bar. I'm going to backtrack and see what, exactly, I broke.
I'm an idiot and let's never speak of this again. (I commented something out by accident and it broke everything and I freaked oh god)
Okay, fixed the crash you got when creating a new Argument and selecting it. The issue was that I was using the make_shared<Assertion> but passing it Arguments expecting it to do the conversion on its own; rather, use make_shared<Argument> and pass it Arguments, and then have it automatically cast to parent when you return it.
I just realized you can't remove links once added! That needs be remedied. Also - the intensity link dialog is working, but when you add a new one it does not automatically add all looser arguments to the stricter one. This should be addressed in intensityLinkCreated or linkIntensity (in mainwindow and outline, respectively).