Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Closures in Formal Languages: Concatenation, Separation, and Algorithms   We continue our study of open and closed languages. We investigate how the
properties of being open and closed are preserved under concatenation. We
investigate analogues, in formal languages, of the separation axioms in
topological spaces; one of our main results is that there is a clopen partition
separating two words if and only if the words commute. We show that we can
decide in quadratic time if the language specified by a DFA is closed, but if
the language is specified by an NFA, the problem is PSPACE-complete.

5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
23
The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga