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[matchstick86]

I declared the library as such:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

and I want to perform the following operation

...
port (c : inout std_logic_vector (5 down to 0);
...
signal a : std_logic_vector (7 downto 0);
...
c(0) <= (a(0) + a(1)); c(1) <= (a(2)+a(3)); c(2) <= (a(4) + a(5)); c(3) <= (a(6) + a(7));
...

I was trying to check behavioural syntax (for simulation) and the error I got was "Found 0 definitions for operator "+"". I've read from other sites that ieee.numeric.std cannot coexist with either ieee.std.logic.arith or ieee.std.logic.unsigned, so that should narrow the problem down a lot more. If I'm not wrong, both c and a are unsigned, so technically they should up.

Unless I am misintepreting std_logic_vector as easily producing different values of c and a. Any help/tips?