title: UML state machine diagram - parallel processes
body: <p>i am trying to develop an UML state machine diagram for the following problem:</p>
  
  <p>a vending machine has 3 buttons: R for 'return money, A &amp; B for drink selections.
  when the vending machine receives amount x of money the user can choose between the drinks. pressing R returns the money without serving a drink. </p>
  
  <p>if a button is pressed before any money is inserted - the machine produces an alarm signal. 
  in case A or B is pressed and >= x money is inserted - the drink will be served.</p>
  
  <p>when serving is done, an alarm sound notifies the user. the change money gets returned. after taking out the drink, the machine goes into the end-state.  </p>
  
  <p><a href="https://i.stack.imgur.com/z9TLh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/z9TLh.png" alt="enter image description here"></a></p>
  
  <p>my issue is that i am working with parallel 'processes' and i believe that there must be a simple configuration for this scenario. can somebody provide/guide me with the right ideas to solve this in an elegant way?</p>
  
  <p>edit: after using the suggestion of @Chris Reynolds i came up with this: </p>
  
  <p><a href="https://i.stack.imgur.com/8guNq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8guNq.png" alt="state machine"></a></p>