val empty : Type.T.t
The empty regular language.
val all : Type.T.t
The language that contains all strings
val allchar : Type.T.t
The language that contains all strings of length 1
range s1 s2 is the language containing all singleton strings (i.e. string of length 1) that are lexicographically beetween
s2 are singleton strings**. Else it is the empty language.