Let A be a finite set. If `f: AvecA` is an onto function, show that `f` is one-one also.

Explanation

To show that if \( f: A \to A \) is an onto function and \( A \) is a finite set, then \( f \) is also one-one, we can follow these steps:

### Step 1: Understand the Definitions
- An **onto function** (or surjective function) means that for every element \( b \) in the codomain \( A \), there exists at least one element \( a \) in the domain \( A \) such that \( f(a) = b \).
- A **one-one function** (or injective function) means that if \( f(a_1) = f(a_2) \), then \( a_1 = a_2 \).

### Step 2: Set the Context
Let \( A \) be a finite set with \( n \) elements. Since \( A \) is finite, we can denote the elements of \( A \) as \( A = \{ a_1, a_2, \ldots, a_n \} \).
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