Re: [isabelle] instance declaration problem with axiomatic classes

Michael Norrish schrieb:
It seems that I cannot do the following

   instance tyop :: (class1, class2) myclass
   <some proof>

   instance tyop :: (class3, class4) myclass
   <some other proof>

where there is no connection between the various class<n>.  This is
despite the fact that the proofs themselves do work.

My reading of the "Order-Sorted Unification" paper suggests to me that
I'm bumping my head against the "unnecessarily strong" co-regularity
condition.  Is there any prospect of this being weakened?

Did I write "unnecessarily strong"? Because I don't think it is. If (during type inference) you unify a type of class myclass with a type "('a,'b) tyop", in your example it is not clear what the classes of the subtypes 'a and 'b should be. You have lost the principal types property.


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