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### Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today. # Why is my answer not being accepted? It works when I enter it in Xcode

I've entered the code into Xcode and it works just fine. What am I doing wrong?

higherOrderFunctions.swift
```/**
For this code challenge, let’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
}

func mathOperation(f: ((Int, Int) -> Int), c: Int, d: Int) -> Int {
return f(c, d)
}
let difference = mathOperation(differenceBetweenNumbers, 9, 7)
``` PLUS

For the sake of this course you should omit the additional parenthesis. Although it works in Xcode, the code check here is a bit picky. Therefore, change your code from

```func mathOperation(f: ((Int, Int) -> Int), c: Int, d: Int) -> Int {
return f(c, d)
}
```

to

```func mathOperation(f: (Int, Int) -> (Int), c: Int, d: Int) -> Int {
return f(c, d)
}
``` Tried this and it is still not working. It is in the second objective where the problem arises where it asks : "Using the differenceBetweenNumbers function as an input to mathOperation, compute the difference between any two integers and assign the result to a constant named difference".