[expr] bit-wise "xor" operator

Arguments must be integers, result is an integer.

Bit ''n'' of the result is 1 if bit ''n'' of the two arguments differ. Otherwise, bit ''n'' of the result is 0.

To evaluate $a^$b when either $a or $b is negative, we make use of the following reasoning:

%| Case | Result |%
%| $a>=0, $b>=0 | Bitwise operation |%

%| $a>=0, $b<0  | $a^$b == ~($a ^ ~$b)        Contrapositive law |%
%|              |       == ~($a ^ (-1-$b))    Extended definition of [~] |%
%|              |       == -1-~($a ^ (-1-$b)) Extended definition of [~] |%
%|              | Since $a and (-1-$b) are both positive, the [^] in the |%
%|              | last expression can be evaluated in bitwise fashion |%

%| $a<0, $b>=0  | Commute to ($b^$a) and evaluate as above. |%

%| $a<0, $b<0   | $a^$b == (~$a) ^ (~$b)     Contrapositive law |%
%|              |       == (-1-$a) ^ (-1-$b) Extended definition of [~] |%
%|              | Since (-1-$a) and (-1-$b) are both positive, the [^] |%
%|              | in the last expression can be evaluated in bitwise |%
%|              | fashion. |%

**Examples**

======
% expr 0b010 | 0b000
2
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[[So, what do I need to add to this example so the result is binary as well?  
Some sort of [format] - but I don't see a binary conversion sequence in the docs...]]
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%|[Category Command]|[Category Syntax]|[Category Mathematics]|%
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