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(add-to-load-path (dirname (current-filename)))
(import
(srfi srfi-41)
(extra-functional)
(my-streams))
(define base (stream-from 1))
(define (f i j)
(+ i j (* 2 i j)))
(define-stream (i-stream i)
(stream-map
(part f i)
(stream-from i)))
(define ij-stream
(stream-let loop ((n 1) (strm (i-stream 1)))
(let* ((next (+ n 1))
(cutoff ((curry >) (stream-car (i-stream next))))
(available (stream-take-while cutoff strm))
(remaining (stream-drop-while cutoff strm)))
(stream-append available (loop next (stream-merge remaining (i-stream next)))))))
(define-stream (sieve input)
(stream-map
(compose (part + 1) (part * 2))
(stream-ordered-diff input ij-stream)))
(define sundaram (stream-cons 2 (sieve base)))
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