entity ent4 is
end entity;

architecture impl of ent4 is
	type bitvv is array(natural range <>) of bit_vector;
	signal foo: bitvv(2 downto 0)(0 downto 0);
	signal bar: bitvv(1 downto 0)(0 downto 0);
begin

foo(2 downto 1) <= bar;
foo(0) <= foo(2);

end architecture;