# Logic and proofs(4/5)

* **Show negation**

![](https://692803005-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LZAnL0SzCN0zyF32Pbe%2F-LZUVlFIeZENuefj-UZG%2F-LZUW5LQC5ykT0nBfnJ6%2F1551011944077.jpg?alt=media\&token=ff87d48d-aa8c-4bbc-9394-7b906e5fdd21)

* **use Demorgan**

1. ∃x ∀y ∃z \~T(x, y, z)

## other example

![](https://692803005-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LZAnL0SzCN0zyF32Pbe%2F-LZXXdoEkVfmT6StlQdZ%2F-LZXYEKs2ckyJgeJFfmv%2F1551062825598.jpg?alt=media\&token=4b1adfbe-15e0-49b4-8163-69d37223929d)

圖中，把集合的陳述，也寫成邏輯陳述．
