Schröder–Bernstein theorem

The Schröder–Bernstein theorem is a fundamental result in set theory concerning the sizes of sets, particularly in relation to their cardinalities. It states that if there are injective (one-to-one) functions between two sets \( A \) and \( B \) such that: 1. There exists an injective function \( f: A \to B \) (embedding of \( A \) into \( B \)), 2.