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# Lesson 9.3: More Sets: Union, Intersections and the Infinity Symbol

## Infinity Symbol

In print, the symbol for infinity is often represented by a figure that looks like the numeral eight in a horizontal position. In braille, this symbol is represented by dot six in the first cell and dots one two three four five six in the second cell.

## Unions and Intersections

The intersection and union symbols are often used with set notation. In print and in braille their configurations are inverses of each other. The braille configuration for the intersection symbol is dots four six dots one four six. The braille symbol for union is dots four six dots three four six. As with any sign of operation, do not space between the intersection and union signs and any symbols which precede or follow them.

### Example 1

$1\phantom{\rule{.3em}{0ex}}\text{to}\phantom{\rule{.3em}{0ex}}\infty$
⠸⠩⠀⠼⠂⠀⠠⠄⠞⠕⠀⠠⠿⠀⠸⠱

### Example 2

$-\infty \phantom{\rule{.3em}{0ex}}\text{to}\phantom{\rule{.3em}{0ex}}+\infty$
⠸⠩⠀⠤⠠⠿⠀⠠⠄⠞⠕⠀⠬⠠⠿⠀⠸⠱

### Example 3

$6+\infty$
⠼⠖⠬⠠⠿

### Example 4

$\text{Does the line go to}\phantom{\rule{.3em}{0ex}}\infty \text{?}$
⠠⠙⠕⠑⠎⠀⠞⠓⠑⠀⠇⠊⠝⠑⠀⠛⠕⠀⠞⠕⠀⠸⠩⠀⠠⠿⠀⠸⠱⠦

### Example 5

$\left[0,\phantom{\rule{.3em}{0ex}}\infty \right)$
⠈⠷⠴⠠⠀⠠⠿⠾

### Example 6

$\left(-\infty ,\phantom{\rule{.3em}{0ex}}20\right]$
⠷⠤⠠⠿⠠⠀⠆⠴⠈⠾

### Example 7

$A\cap B$
⠠⠁⠨⠩⠠⠃

### Example 8

$A\cup B$
⠠⠁⠨⠬⠠⠃

### Example 9

${A}^{\prime }\cup B$
⠠⠁⠄⠨⠬⠠⠃

### Example 10

$X\cap Y=\varnothing$
⠠⠭⠨⠩⠠⠽⠀⠨⠅⠀⠸⠴