Title
The WHILE Hierarchy of Program Schemes Is Infinite
Abstract
We exhibit a sequence Sn (n � 0) of while program schemes, i. e., while programs without interpretation, with the prop- erty that the while nesting depth of Sn is n, and prove that any while program scheme which is scheme equivalent to Sn, i. e., equivalent for all interpretations over arbitrary domains, has while nesting depth at least n. This shows that the while nesting depth imposes a strict hier- archy (the while hierarchy) when programs are compared with respect to scheme equivalence and contrasts with Kleene's classical result that every program is equivalent to a program of while nesting depth 1 (when in- terpreted over a fixed domain with arithmetic on non-negative integers). Our proof is based on results from formal language theory; in particular, we make use of the notion of star height of regular languages.
Year
DOI
Venue
1998
10.1007/BFb0053540
FoSSaCS
Keywords
Field
DocType
program schemes,formal language,regular language
Integer,Discrete mathematics,Combinatorics,Formal language,Star height,Contrast (statistics),Equivalence (measure theory),Regular language,Hierarchy,Mathematics
Conference
Volume
ISSN
ISBN
1378
0302-9743
3-540-64300-1
Citations 
PageRank 
References 
1
0.35
9
Authors
2
Name
Order
Citations
PageRank
Can Adam Albayrak143.17
Thomas Noll2236.12