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Error code: VFAV(2)

Error: alias clause lists a bracket alias for a feature that is not a query
  with at least one argument or class has other feature with bracket alias.
What to do: ensure that class has at most one feature with bracket alias
  and that this feature is a query with at least one argument.

Class: AA
Feature name: f
Line: 16
      
->  f alias "[]": BOOLEAN
      do

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