if
is the set of all strings that machine
accepts, we say that
is the language of machine
and write
. we say that
recognizes
or that
accepts
. because the term accept has different meanings when we refer to machines accepting strings and machines accepting languages, we prefer the term recognize for languages in order to avoid confusion.
a machine may accept several strings, but it always recognizes only one language. if the machine accepts no strings, it still recognizes one language–namely, the empty language
.