We recall the notion of regular closure of classes of languages. We present
two important results. The first result is that all languages which are in
the regular closure of the class of deterministic (context-free) languages
can be recognized in linear time. This is a nontrivial result, since this
closure contains many inherently ambiguous languages. The second result is
that the class of deterministic languages is contained in the closure of th
e class of deterministic languages with the prefix property or, stated in a
n equivalent way, all LR(k) languages are in the regular closure of the cla
ss of LR(0) languages.