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Error code: VAPE

Error: some clients have access to routine but not to a feature used in
  its precondition.
What to do: make sure that all features used in the precondition
  are exported to all the clients to which routine is available.

Class: AA
Feature: f
Insufficiently exported feature: forth from BB
Line: 21
      require
->      across b as c all True end
      do

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