3) Backslash before keywords looks inspired by TeX to me.
On an unrelated note, this-is-a-valid-identifier also in Lisp, but weirdly enough, the parens "( )" require shift. I think Lisp should use "[ ]" as parens because they do not require shift on modern keyboards.
I switch the layout of my non English keyboard in all coding windows and my fingers know what to press there.
> [define [plus i j] [+ i j]]
> [plus 1 2]
3