If you want to be able to write practically anything on mobile, including ≠, ≈, ‰, ℝ etc., have a look at Unexpected keyboard. No spellcheck or autocomplete, though.

In a considerable part of the world. https://en.m.wikipedia.org/wiki/List_of_minimum_driving_ages

Thanks for this, those are some incredible designs!

I very much like Unexpected keyboard. It takes a bit of work, but you can completely change the layout, sizes of all buttons, and one button can contain multiple characters. You input all the extra ones by swiping from the key in a particular direction, which is very fast and convenient. Plus it has an easy access to input of many, many special characters, contains Ctrl, you can have gestures for copy/paste/undo and so on. But it doesn’t have any predictions yet, you have to type everything out.

This doesn’t sound very accurate. For starters, classical mechanics fails to describe even motion of Mercury. But more importantly, uncertainty in this context means someting else in this context. And while it is true that Schrödinger’s cat is both alive and dead until observed, once observed, it’s been dead or alive all along. Same with a tree, once it is determined it has fallen, it has already made the sound and produced all the consequences some time ago. While I don’t understand quantum mechanics, I’m fairly sure the person who wrote the copypasta understands it even less than me.