title: How to show that union and intersection of min cuts in flow network is also a min cut
body: <p>The proof of this is everywhere skipped and said to be corollary of Min-Cut-Max-Flow theorem ... It's usually something like:</p>
  
  <p>Let S1 and S2 be minimum cuts of a flow network. Then S1∪S1 and S1∩S2 are also min cuts.</p>
  
  <p>Can anyone tell me how exactly this is proved?</p>