$A \rightarrow( B \to A )$
$\equiv A \to(\sim B \vee A )$
$\equiv \sim A \vee(\sim B \vee A )$
$\equiv(\sim A \vee A ) \vee \sim B$
$\equiv T \vee \sim B \equiv T$
$\therefore T \vee B = T$
$\equiv(\sim A \vee A ) \vee B$
$\equiv \sim A \vee( A \vee B )$
$\equiv A \to( A \vee B )$