## Functions or Not?

**Objective**

In this problem, we touch upon a basic concept that is fundamental to Functional Programming: identifying a relation which represents a valid function.

**Task**

You are given a set of unique ordered pairs constituting a relation. The -values form the domain, and the -values form the range to which they map. For each of these relations, identify whether they may possibly represent a valid *function* or not.

**Note:** You do not have to find the *actual* function, you just need to determine that the relation may be representative of some valid function.

**Input Format**

The first line contains an integer, , denoting the number of test cases. The subsequent lines describe test cases, and the input for each test case is as follows:

- The first line contains an integer, , the number of pairs in the test case.
- The subsequent lines each contain two space-separated integers describing the respective and values for each ordered pair.

**Constraints**

- N

**Output Format**

On a new line for each test case, print if the set of ordered pairs represent a valid function, or if they do not.

**Sample Input**

```
2
3
1 1
2 2
3 3
4
1 2
2 4
3 6
4 8
```

**Sample Output**

```
YES
YES
```

**Explanation**

*Test Case 0:*

, Ordered Pairs:
The set of ordered pairs represents a relation, which could represent a function such as , . Thus, we print on a new line.

*Test Case 1:*

, Ordered Pairs:

The set of ordered pairs represents a relation, which could represent a function such as , . Thus, we print on a new line.