In GO, a function is also a type. Two functions are of the same type if they have the same arguments and the same return values.

When passing a function as an argument to another function, the exact signature of the function must be specified in the argument list.

// Here, the Arithmetic function receives
// as an argument a function that
// must have the form of func(int, int) int.
func Arithmetic(x, y int, f func(int, int) int) int {
    return f(x, y)
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// The Add function can be
// passed to the Arithmetic function,
// as it has the required form, or signature.
func Sum(x, y int) int {
    return x + y
}