[GHC] #13822: GHC not using injectivity?

[GHC]

#13822: GHC not using injectivity?
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  fixed             |             Keywords:
                                     |  InjectiveFamilies, TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Would someone like to add it as a regression test?  It never does any
 harm!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13822#comment:4>
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