Union of two sets in Scala

Question

From the question linked here, I found this implementation of Union in Scala:

def union(a: Set, b: Set): Set = i => a(i) || b(i)

And Set is

Answer 1

Let say we have object called SoSet given by

object SoSet {
    type Set = Int => Boolean
    val a : Set = ???
    val b : Set = ???
    def isItem(item : Int) = a(item) || b(item)
}

The signature of isItem is given by Int => Boolean which is a Set. So far so good.

But now we just want to return the function isItem (i.e. a Set).

So lets define union function for this (There are no parameters right now. We will add it later).

object SoSet {
    //..   
     def union : Set = isItem // returns the function isItem
}

Now lets refactor the isItem into a anonymous function.

object SoSet {
    //..   
    def union : Set = {
      (item : Int) => a(item) || b(item)
    }
}

Lets move Set a and b from object SoSet to parameters of def union. Refactor item to i.

object SoSet { 
   type Set = Int => Boolean
   def union(a : Set, b : Set) : Set = (i : Int) => a(i) || b(i)
}

UPDATE

 val s1 = Set(1, 2, 3)                           
 val s2 = Set(2, 3, 4)     
 val s3 = union(s1, s2) //  returns the function..  Int => Boolean = 
 s3(2)  // invokes the function & checks if 2 is present in the union