The Functions or Not? problem is defined as follows:

You are given a set of unique (x, y) ordered pairs constituting a relation. For each of these relations, identify whether they may possibly represent a valid function or not. On a new line for each test case, print YES if the set of ordered pairs represent a valid function, or NO if they do not.

The definition of the function helps to get the idea on how to solve this problem (from Wikipedia):

*In mathematics, a function is a relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output.*

This property holds for the both sample inputs so they result in YES. There is no sample negative input. It should be crafted in order to test the code:

```
2
2
1 2
2 3
2
1 1
1 2
```

There is a function for the first set of pairs and there is no function for the second set.

F# solution:

```
open System
[<EntryPoint>]
let main argv =
let t = Console.ReadLine () |> int
seq { for _ in 1..t do
let n = Console.ReadLine () |> int
yield seq { for _ in 1..n do
yield (Console.ReadLine ()).Split(' ') }
|> Seq.groupBy (fun v -> v.[0])
|> Seq.forall (fun v -> 1 = ((snd v)
|> Seq.map (fun q -> q.[1])
|> Seq.distinct
|> Seq.length))
|> function | true -> "YES" | _ -> "NO" }
|> Seq.iter (printfn "%s")
0 // return an integer exit code
```