; not quite right, because behavior of underlying eqv unspecified
; in many cases according to r5rs
; do we really want is to ret t for distinct strings?

(xdef 'is (lambda args
            (tnil (or (all (lambda (a) (eqv? (car args) a)) (cdr args))
                    (and (all string? args)
                         (apply string=? args))
                    (all ar-false? args)))))

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