Combinatorial and Recursive Aspects of the Automorphism Group of the Countable Atomless Boolean Algebra
Madison, E. W. ; Zimmermann-Huisgen, B.
J. Symbolic Logic, Tome 51 (1986) no. 1, p. 292-301 / Harvested from Project Euclid
Given an admissible indexing $\varphi$ of the countable atomless Boolean algebra $\mathscr{B}$, an automorphism $F$ of $\mathscr{B}$ is said to be recursively presented (relative to $\varphi$) if there exists a recursive function $p \in \operatorname{Sym}(\omega)$ such that $F \circ \varphi = \varphi \circ p$. Our key result on recursiveness: Both the subset of $\operatorname{Aut}(\mathscr{B})$ consisting of all those automorphisms which are recursively presented relative to some indexing, and its complement, the set of all "totally nonrecursive" automorphisms, are uncountable. This arises as a consequence of the following combinatorial investigations: (1) A comparison of the cycle structures of $f$ and $\bar{f}$, where $f$ is a permutation of some free basis of $\mathscr{B}$ and $\bar{f}$ is the automorphism of $\mathscr{B}$ induced by $f$. (2) An explicit description of the permutations of $\omega$ whose conjugacy classes in $\operatorname{Sym}(\omega)$ are (a) uncountable, (b) countably infinite, and (c) finite.
Publié le : 1986-06-14
Classification: 
@article{1183742094,
     author = {Madison, E. W. and Zimmermann-Huisgen, B.},
     title = {Combinatorial and Recursive Aspects of the Automorphism Group of the Countable Atomless Boolean Algebra},
     journal = {J. Symbolic Logic},
     volume = {51},
     number = {1},
     year = {1986},
     pages = { 292-301},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1183742094}
}
Madison, E. W.; Zimmermann-Huisgen, B. Combinatorial and Recursive Aspects of the Automorphism Group of the Countable Atomless Boolean Algebra. J. Symbolic Logic, Tome 51 (1986) no. 1, pp.  292-301. http://gdmltest.u-ga.fr/item/1183742094/