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A089861
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Permutation of natural numbers induced by Catalan Automorphism *A089861 acting on the binary trees/parenthesizations encoded by A014486/A063171.
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13
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0, 1, 3, 2, 7, 8, 4, 6, 5, 17, 18, 20, 21, 22, 9, 10, 14, 16, 19, 11, 15, 12, 13, 45, 46, 48, 49, 50, 54, 55, 57, 58, 59, 61, 62, 63, 64, 23, 24, 25, 26, 27, 37, 38, 42, 44, 47, 51, 53, 56, 60, 28, 29, 39, 43, 52, 30, 40, 31, 32, 33, 41, 34, 35, 36, 129, 130, 132, 133, 134, 138
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OFFSET
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0,3
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COMMENTS
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This automorphism effects the following transformation on the unlabeled rooted plane binary trees (letters A, B, C refer to arbitrary subtrees located on those nodes and () stands for an implied terminal node).
.A...B...............A...C
..\./.................\./
...x...C...-->.....B...x...............()..A.........A..()..
....\./.............\./.................\./....-->....\./...
.....x...............x...................x.............x....
((a . b) . c) --> (b . (a . c)) ____ (() . a) ----> (a . ())
See the Karttunen OEIS-Wiki link for a detailed explanation of how to obtain a given integer sequence from this definition.
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LINKS
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PROG
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(Scheme functions implementing this automorphism on list-structures/S-expressions, both constructive (*A089861) and destructive (*A089861!) versions:)
(define (*A089861 s) (cond ((not (pair? s)) s) ((not (pair? (car s))) (cons (cdr s) (car s))) (else (cons (cdar s) (cons (caar s) (cdr s))))))
(define (*A089861! s) (cond ((pair? s) (cond ((pair? (car s)) (swap! (car s)) (robr! s)) (else (swap! s))))) s)
(define (swap! s) (let ((ex-car (car s))) (set-car! s (cdr s)) (set-cdr! s ex-car) s))
(define (robr! s) (let ((ex-cdr (cdr s))) (set-cdr! s (caar s)) (set-car! (car s) ex-cdr) (swap! (car s)) (swap! s) s))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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A graphical description and constructive version of Scheme-implementation added by Antti Karttunen, Jun 04 2011
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STATUS
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approved
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