[expr] bit-wise "or" operator

Arguments must be integers, result is an integer.

Bit ''n'' of the result is 0 if bit ''n'' of each argument is 0. Otherwise, bit ''n'' of the result is 1.

For negative arguments, observe that ~$n[==](-1-n) (See the [~] operator for further discussion.)  The following cases then exist:

%| Case | Result |%
&| `$a>=0,$b>=0` | `$a<<pipe>>$b`, as defined above. |&
&| `$a>=0,$b<0` | `$a<<pipe>>$b == ~(~$a & ~$b)` ''De Morgan's Law'' <<br>>`$a<<pipe>>$b == ~(~$a & (-1-$b))` ''Extended definition of [~]'' <<br>>`$a<<pipe>>$b == -1-(~$a & (-1-$b))` ''Extended definition of [~]'' <<br>>The expression (-1-$b) is nonnegative, and so the expression ([~]$a [&] ([-]1-$b)) can be evaluated by bitwise operations. |&
&| `$a<0,$b>=0` | Commute to (`$b <<pipe>> $a`) and solve as above. |&
&| `$a<0,$b<0` | `$a<<pipe>>$b == ~(~$a & ~$b)` ''De Morgan's Law'' <<br>>`$a<<pipe>>$b == -1-((-1-$a) & (-1-$b))` ''Extended definition of [~]'' <<br>>Since ([-]1-$a) and (-1-$b) are both nonnegative, the [&] in the expression above can be evaluated wuth bitwise operations. |&

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