** Subset Equality Problem:** Given a set

**S**of non-negative integer values, the problem is to identify if there is a partition of the set

**S**into two sets

**X**and

**Y**, such that, the integer sum in

**X**is equal to the sum of integers in

**Y**.

__Explanation__:

An instance of the problem is an input specified to the problem. An instance of the **Subset Equality Problem** is a set **S**. Since an NP-Complete problem is a problem which is both in **NP** and **NP-hard**, the proof for the statement that a problem is NP-Complete consists of two parts:

- The problem itself is in
NP class.- All other problems in NP class can be polynomial-time reducible to that.(B is polynomial-time reducible to C is denoted as B ≤ P
^{C})

If the **2nd condition** is only satisfied then the problem is called **NP-Hard**.

But it is not possible to reduce every NP problem into another NP problem to show its NP-Completeness all the time. Therefore, to show a problem is NP-Complete, then proof that the problem is in **NP** and any **NP-Complete problem** is reducible to that i.e., if B is NP-Complete and B ≤ P^{C} then for C in NP, then C is NP-Complete. Thus, it can be concluded that the **Subset Equality Problem** is NP-Complete using the following two propositions:

**Subset equality is in NP****Subset equality is NP-Hard**

This two proposition can be proved as the **Subset Equality Problem** is a special case of the **Subset Sum Problem** where the sum of each partition of subset **X** and **Y **in **S** can be set as:

Since the subset-sum is **NP-Complete**, the subset equality problem also becomes **NP-Complete**.

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