1 | initial version |

It is obvious that $x \leq 0$ if and only if it is not the case that $x<0$. So, we can write

```
not(x.is_negative())
```

2 | No.2 Revision |

It is obvious that $x ~~\leq ~~\geq 0$ if and only if it is not the case that $x<0$. So, we can write

```
not(x.is_negative())
```

Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.