> As a data type, are keywords a subtype of symbols or disjoint from
> them?  I think they are generally a subtype, but they are disjoint in
> Chicken.  Presumably they are disjoint in Racket and Kawa as well.

Racket:

(keyword? '#:foo)       => #t
(symbol? '#:foo)        => #f

Kawa:

(keyword? '#:foo)       => #t
(symbol? '#:foo)        => #t
(symbol->string '#:foo) => "foo:"
'foo:                   => foo:
(keyword? 'foo:)        => #t
(eqv? 'foo: ':foo)      => #f
(eqv? 'foo: '#:foo)     => #t

https://www.gnu.org/software/kawa/Keywords.html