Just to expand a bit, ` is _not_ a syntax to declare an lfun. It's
just a syntax to create certain identifiers not conforming to the
usual letters-and-numbers form. Kind of like the | character in
Common LISP. You can use such identifiers anywhere, for example
int `< = 3;
is a correct declaration of a local variable.
A method is treated like an lfun iff its name matches one of the
existing lfun names. Not all lfuns have names using the ` form (for
example "_indices" and "_values" do not), and not all names on the `
form are lfuns (examples include your "`<=", and things like "```!"
(no lfun currently has a name with more than two ` at the beginning)).
