Created
September 27, 2011 05:43
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relation algebra
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| (define (zip-cons a b) | |
| (if (null? a) | |
| '() | |
| (cons (cons (car a) (car b)) | |
| (zip-cons (cdr a) (cdr b))))) | |
| (define (p c r) | |
| (cond | |
| ((null? c) (map (lambda (x) '()) r)) | |
| ((eq? (car c) (caar r)) | |
| (zip-cons | |
| (map car r) | |
| (p (cdr c) (map cdr r)))) | |
| (else (p c (map cdr r))))) |
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