# Subsets and sets symbol explenation (Very simple question please have a look)

## Homework Statement

Hi
I would like you please to look my attachement ,and explain to me the meaning of the line above M and N whats the meaning of this line?It seems to me that it acts as we should take the complementary collection of numbers .

## The Attempt at a Solution

#### Attachments

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Yes, you are probably right. The notation $\overline{N}$ just means all the elements which are not in N.