### 2. 书写一个质能守恒公式[^LaTeX]
$$E=mc^2$$
### 3. 高亮一段代码[^code]
```python
@requires_authorization
class SomeClass:
pass
if __name__ == '__main__':
# A comment
print 'hello world'
```
### 2. 书写一个质能守恒公式[^LaTeX]
$$E=mc^2$$
### 3. 高亮一段代码[^code]
```python
@requires_authorization
class SomeClass:
pass
if __name__ == '__main__':
# A comment
print 'hello world'
```