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Swift Closures.

I have no idea where is my problem:(.

higherOrderFunctions.swift
```/**
For this code challenge, letβs define a math operation as a function that
carries out some work on two integers and returns an integer as well. An
example is the function below, `differenceBetweenNumbers`, which takes two
integers and calculates the difference between the numbers. After calculating,
it returns the difference.
*/

func differenceBetweenNumbers(a: Int, b:Int) -> (Int) {
return a - b
}

```

Hey Andrey Mitko,

This challenge wants you to make a higher order function. The function takes in a function as the first parameter (a math operation), and then two integers to evaluate on as the second and third parameters. So our first parameter has to have the same function signature as the differenceBetweenNumbers function (Int, Int) -> Int.

We then call this higher order function, mathOperation, by passing it three arguments.

1. a math operation (Int, Int) -> Int

2. an integer, Int

3. another integer, Int

Note that the names of these arguments are not used when calling the function. This is because we have omitted the external parameter names by using an underscore before the local parameter name. The first parameter does not need an underscore because it omits the external parameter name by default.

```func differenceBetweenNumbers(a: Int, b:Int) -> (Int) {
return a - b
}