bug in some assertions in `chemistry.rs`

[moritz-gross]

Some assertions in chemistry.rs have a ! in the front, which I assume should be logical negation.
But as .len() returns a value of type usize, the ! operator is the bitwise flip.
And as usize is the unsigned type, it's basically impossible to land at the value 0 or 1 using bitwise flipping.

Is this some kind of bug in a bug situtation, as to why it has not shown up yet?

I guess the chemistry section is not really a priority right now anyway, I was just poking around in the file as I recently talked to a friend doing his Chemistry PhD, so I was interested in what I could find here ;)

Here is one such example from the code:

fn is_structural(elements: &[&str]) -> bool {
    assert!(!elements.len() > 1);   // already handled