Every ${\rm low}\sb 2$ Boolean algebra has a recursive copy

Every Low 2 Boolean Algebra Has a Recursive Copy

The degree of a structure si is the Turing degree of its open diagram £»(j/) , coded as a subset of a>. Implicit in the definition is a particular presentation of the structure; the degree is not an isomorphism invariant. We prove that if a Boolean algebra si has a copy of low 2 degree, then there is a recursive Boolean algebra 33 which is isomorphic to si . This builds on work of Downey and Jo...

A Model in Which Every Boolean Algebra Has Many Subalgebras

We show that it is consistent with ZFC (relative to large cardinals) that every infinite Boolean algebra B has an irredundant subsetA such that 2|A| = 2|B|. This implies in particular that B has 2|B| subalgebras. We also discuss some more general problems about subalgebras and free subsets of an algebra. The result on the number of subalgebras in a Boolean algebra solves a question of Monk from...

Every Body Has a Brain

[1] http://ebhb.morphonix.com/ [2] http://fireflyfoundation.wordpress.com/brain-games/every-body-has-a-brain/ [3] http://dev.cdgr.ucsb.edu/organizations/morphonix [4] http://dev.cdgr.ucsb.edu/category/genre/educational [5] http://dev.cdgr.ucsb.edu/category/genre/music/dance [6] http://dev.cdgr.ucsb.edu/category/topics/anatomy [7] http://dev.cdgr.ucsb.edu/category/topics/brain [8] http://dev.cdg...

Every Algorithm Has a POV

Every Poset Has a Central Element

It is proved that there exists a constant 6, f > 6 > 0, such that in every finite partially ordered set there is an element such that the fraction of order ideals containing that element is between 6 and 1 -6. It is shown that 6 can be taken to be at least (3-log, 5)/4~0.17. This settles a question asked independently by Colburn and Rival, and Rosenthal. The result implies that the information-...