Error: A features result type was redefined differently.
  This error occurs only in the context of multi constraints
  with flat class checking enabled.

What to do:
  Consider the following example:

    class A
    feature
      f: ANY
    end

    class B
      inherit A redefine f end
    feature
      f: INTEGER
    end

    class C
      inherit A redefine f end
    feature
      f: STRING
    end
	  
    class NON_MULTI
    feature
      a: A
      example: ANY
        do
          Result := a.f.is_equal (3) -- @1
        end
    end

    class MULTI [G -> {B, C}]
      inherit NON_MULTI redefine a end
    feature
      a: G
    end

  The problem is that in the context of `MULTI' the feature
  `example' has an ambigous call @1. This is because f occurs
  redefined in B and C and, assuming that the signature of
  `is_equal' is `like Current' this would yield to a CAT call
  in case an actual formal derivation would not select the
  version of from B but the one from C (which is STRING,
  not INTEGER). So what you can do is change the signature or
  the constraints or reimplement the feature.