O What's the last slash? A symbol in mathematics, which means empty set. An empty set is a collection without any elements. An empty set is a subset of all sets; Is any non-empty set of proper subset.

You can type with special symbols of sogou input method. The specific steps are as follows:

1, switch the computer input method to sogou input method;

2. Then place the mouse cursor at any position in the status bar of sogou input method, and then click the right mouse button;

3. On the pop-up page, click "Expression &; Symbol ";

4. Click "Symbol Daquan" again;

5. After entering the symbol encyclopedia, click "Mathematics/Unit" on the left, and then what is the last one in the third line on the right? Ok, you can type it with a click.

Baidu encyclopedia-?