Let$\DeclareMathOperator\Card{Card}$Let $A$ be an arbitraryinfinite set, $A$ is not finite, and let $B=\{X\subset A | Card(X)<Card(A)\}$$B=\{X\subset A \mid \Card(X)<\Card(A)\}$. Can it be proven that $Card(A)=Card(B)$$\Card(A)=\Card(B)$?
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