
(define supported make-depends)
(define more-informative-supports? more-informative-needs?)

(define contingent make-depends)
(define contingent? depends?)
(define ->contingent ->depends)
(define contingent-able? depends-able?)
(define contingent-info  depends-info)
(define contingent-premises depends-premises)

(define v&s-> v&d->)
(define v&s-equivalent? v&d-equivalent?)
(define v&s-support v&d-needs)
(define v&s-value v&d-value)
(define v&s? v&d?)

(define ???? #f)