Linking issue rules

[Jon]

hi

im trying to figure out how i can make a rule the prohibits an issues from being linked together if one of the fields is not the same (i.e. location).

I have two type of issues. contracts and shipments. I was also trying to make a rule that would only allow a shipment to be linked to one contract max. However multiple shipments could be applied to the same contract. 

 jon