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Linglib.Theories.Semantics.Dynamic.Core.DRSExpr

DRS Syntax: Discourse Representation Structures #

@cite{kamp-reyle-1993} @cite{muskens-1996}

Pure syntactic representation of DRS expressions with structural operations — no semantic imports, no interpretation.

Definitions #

Design #

This module is the pure-syntax layer of the four-layer dynamic semantics architecture:

DynProp.lean       ← semantic algebra (DRS S, dseq, test, ...)
DynamicTy2.lean    ← compositional layer (Dref, AssignmentStructure)
DRSExpr.lean       ← DRS syntax (this file)
Accessibility.lean ← interpretation bridge (DRSExpr → DRS)

DRSExpr has no dependency on the semantic algebra (DRS S) or compositional types (Dref, Assign). Interpretation is defined in Accessibility.lean via interp : DRSExpr → DRS (Assign E).

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inductive Semantics.Dynamic.Core.DRSExpr.DRSExpr :
Type

Syntactic representation of DRS expressions.

Dref indices are natural numbers. Relation symbols are identified by natural number indices; their arity is implicit in the dref list.

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    instance Semantics.Dynamic.Core.DRSExpr.instReprDRSExpr :
    Repr DRSExpr
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    partial def Semantics.Dynamic.Core.DRSExpr.instReprDRSExpr.repr :
    DRSExpr → Nat → Std.Format
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    def Semantics.Dynamic.Core.DRSExpr.adr :
    DRSExpr → List Nat

    Active discourse referents: the drefs introduced by K.

    adr([u₁,...,uₙ | γ₁,...,γₘ]) = {u₁,...,uₙ} adr(K₁ ; K₂) = adr(K₁) ∪ adr(K₂)

    Conditions (atoms, negation, disjunction, implication) introduce no drefs.

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      def Semantics.Dynamic.Core.DRSExpr.occurs (u : Nat) :
      DRSExpr → Bool

      Whether dref u occurs anywhere in expression K.

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        def Semantics.Dynamic.Core.DRSExpr.occurs.occursAny (u : Nat) :
        List DRSExpr → Bool
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          def Semantics.Dynamic.Core.DRSExpr.acc (u : Nat) :
          DRSExpr → List Nat

          Accessible drefs from an occurrence of u in K.

          Defined by structural recursion following @cite{muskens-1996} pp. 170–171:

          • Atomic: no drefs are accessible
          • Negation: accessibility passes through
          • Disjunction/implication: accessibility from the branch containing u, with antecedent drefs accessible in the consequent
          • Box: new drefs are accessible, plus accessibility from the condition containing u
          • Sequencing: drefs from K₁ are accessible in K₂
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            def Semantics.Dynamic.Core.DRSExpr.acc.accFind (u : Nat) :
            List DRSExpr → Option (List Nat)

            Find the first condition containing u and return its accessible drefs.

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              def Semantics.Dynamic.Core.DRSExpr.allOccurring :
              DRSExpr → List Nat

              Collect all dref indices mentioned anywhere in K.

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                def Semantics.Dynamic.Core.DRSExpr.allOccurring.allOccurringList :
                List DRSExpr → List Nat
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                  def Semantics.Dynamic.Core.DRSExpr.isFree (u : Nat) (K : DRSExpr) :
                  Bool

                  A dref u is free in K if it occurs in K but is not among the drefs accessible from its position.

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                    def Semantics.Dynamic.Core.DRSExpr.isProper (K : DRSExpr) :
                    Bool

                    A DRS is proper if it contains no free referents (@cite{muskens-1996}, p. 171).

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                      def Semantics.Dynamic.Core.DRSExpr.exManAdoresWoman :
                      DRSExpr

                      "A man adores a woman" as a syntactic DRS.

                      [u₁ u₂ | man u₁, woman u₂, u₁ adores u₂]

                      Using relation indices: 0 = man, 1 = woman, 2 = adores.

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                      • One or more equations did not get rendered due to their size.
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                        def Semantics.Dynamic.Core.DRSExpr.exDonkey :
                        DRSExpr

                        "If a farmer owns a donkey, he beats it" as a syntactic DRS.

                        [u₁ u₂ | farmer u₁, donkey u₂, u₁ owns u₂] ⇒ [| u₁ beats u₂]

                        Using relation indices: 0 = farmer, 1 = donkey, 2 = owns, 3 = beats.

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                        • One or more equations did not get rendered due to their size.
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                          def Semantics.Dynamic.Core.DRSExpr.exFree :
                          DRSExpr

                          "He₁ stinks" (with no antecedent) is NOT proper: dref 1 is free.

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