<div class="solution">
<center> Card (A \cup B) \leq Inf(a+b,n)</center> 
  
<center> Card (A \cap B) \leq b</center>
 
<center> Card (A \cup B) \geq a</center>  

<center> Card (A \cap B) \geq Sup(0,a+b-n)</center> 
</div>
