[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 |
|             |       == ~(~$a & (-1-$b))    Extended definition of [~] |
|             |       == -1-(~$a & (-1-$b))  Extended definition of [~] |
| | 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 |
|            |       == -1-((-1-$a) & (-1-$b)) Extended definition of [~] |
| | Since (-1-$a) and (-1-$b) are both nonnegative, the & in the expression above can be evaluated wuth bitwise operations. |

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