Theorem : There is a recursive language that is not context-sensitive.
Proof : Let us first enumerate all the halting TMs for the CSLs over the alphabet 
={0, 1}. To represent every CSG G is completely specified by its production 
, i=1,2, 3, ---, m and hence can be represented as a string.
we can apply the following homomorphism to the above string to construct the unique binary encoding of G.
h(0) = 010 |
h(1) = 0120 |
h(  ) = 0130 |
h(#) = 0140 |
, 
where 
is the set of nonterminal of G.