As the given condition dictates: "begins with z, x in the middle and ends with y" and the min_length = 4 characters...
Here is your regex without commas:
RE = ( z x x y )*
The language over Σ = {x, y, z} according to this RE will be:
L = { ^, zxxy, zxxyzxxy, zxxyzxxyzxxy, ... }
The length of first string is ZERO because null string doesn't have any characters in it i.e. condition violated...
Second string is okay...
Third string has y and z along with x's in it...
Fourth string also has y's and z's along with x's in it...
And, so on...
It is quite obvious that the RE: ( z x x y )* cannot generate the required language as described in the problem statement...
i hav found ds solutn. if there is any mstak plz reply