A question about search

[Dauphin]

I notice the options:

Search for items including these words:
and excluding these words:
and optionally containing these words:
search for exact phrase:


What purpose does the third option serve? It appears a little redundant. I think it has a function - the OR function is what I think its supposed to be but the wording is confusing.

[MarkG]

if the first option is A and the third is B, if you use both you'll have the following expresion

(A and B) or (A)

[Ljube]

Originally posted by MarkG
if the first option is A and the third is B, if you use both you'll have the following expresion

(A and B) or (A)

Which is logically equivalent to A.


The proof:

Assume A is true. Then (A and B) or (A) is true.
Assume A is false. Then (A and B) is false, hence (A and B) or (A) is false.
Assume B is true/false - no bearing on the logical value of the expression (A and B) or (A).

[DrSpike]

Just how bored were you when you noticed this BC? :)

[MarkG]

Originally posted by Ljube-ljcvetko
Which is logically equivalent to A.

The proof:

Assume A is true. Then (A and B) or (A) is true.
Assume A is false. Then (A and B) is false, hence (A and B) or (A) is false.
Assume B is true/false - no bearing on the logical value of the expression (A and B) or (A). perhaps , but you also get results with the B text highlighted :)

[Dauphin]

Ok that makes some sense. You get to highlight options without filtering negative results.