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minimal_over_approximation (509B)

      1 # Minimal over approximation
      2 
      3 A *minimal over approximation* with property P is an [over_approximation] Q' of Q having property P such that any query having property P in which Q is [query_contained] in Q is such that Q' is also [query_contained] in it
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      5 For [CQs], minimal over approximations do not always exist, and the decidability of their existence is open except in special cases, cf [morvan2025homomorphism] p133 and [barcelo2020more]
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      7 Up: [over_approximation]
      8 
      9 See also: [maximal_under_approximation]