Explanation facilities for symmetric DANs

[Francisco Javier Díez]

All the explanation options available for influence diagrams should also be available for symmetric DANs. There are two possibilities:

• Activating the thunder button only for symmetric DANs (it requires checking after each edit whether the DAN is symmetric)
• Having that button always active and showing a message when the user clicks on it and the DAN is not symmetric.

I think the second option is easier to implement and more informative for the user, especially if the message points out the reason for the assymetry.

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