In 1969 Rabin introduced tree automata and proved one of the deepest decidability results. If you worked on decision problems you did most probably use Rabin's result. But did you make your way through Rabin's cumbersome proof with its induction on countable ordinals? Building on ideas of our predecessors-&-mdash;and especially those of… (More)
We show that if A and A are automorphic via then the structures S R (A) and S R (A) are 0 3-isomorphic via an isomorphism induced by. Then we use this result to classify completely the orbits of hhsimple sets.
Telescopes and imaging interferometers with sparsely filled apertures can be lighter weight and less expensive than conventional filled-aperture telescopes. However, their greatly reduced MTF's cause significant blurring and loss of contrast in the collected imagery. Image reconstruction algorithms can correct the blurring completely when the… (More)
A set X of nonnegative integers is computably enumerable (c.e.), also called recursively enumerable (r.e.), if there is a computable method to list its elements. Let E denote the structure of the computably enumerable sets under inclusion, E = (fW e g e2! ;). We previously exhibited a rst order E-deenable property Q(X) such that Q(X) guarantees that X is… (More)
Post 1944 began studying properties of a computably enumerable (c.e.) set A such as simple, h-simple, and hh-simple, with the intent of nding a property guaranteeing incompleteness of A. From observations of Post 1943 and Myhill 1956, attention focused by the 1950's on properties deenable in the inclusion ordering of c.e. subsets of !, namely E =… (More)