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Best answer
57 votes
57 votes

$R-(R-S)$

There is no need to use Union operator here.

Just because they say you can use operators from $(∪, −)$ we don't need to use both of them.

Also they are saying that only the minimum number of operators from (∪, −) which is equivalent to $R ∩ S$.

My expression is Minimal.

edited by
15 votes
15 votes
Answer: R − ((R ∪ S) − S)

Just imagine the Venn diagram in mind.
0 votes
0 votes
p ={(1,1) , (2,2) , (1,2)}

q={(1,2) , (2,10) ,(3,2)}

p ח q = { (1,2) }

p-q={ (1,1) (2,2) }

p-(p-q) = { (1,2) }

so  p-(p-q) = p ח q = { (1,2) }

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