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Semantics for ML

Building counter-interpretations with possible worlds and accessibility to show modal entailment claims fail in systems such as K and S4.

forall x: Calgary, Semantics for ML

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3 exercises

Exercise A

Present counter-interpretations to the following:

  1. ¬P⊨K¬◊P\neg P\vDash_{\mathbf{K}}\neg\Diamond P

  2. □(P∨Q)⊨K□P∨□Q\Box(P\vee Q)\vDash_{\mathbf{K}}\Box P\vee\Box Q

  3. ⊨K¬□(A∧¬A)\vDash_{\mathbf{K}}\neg\Box(A\wedge\neg A)

  4. □A⊨KA\Box A\vDash_{\mathbf{K}}A

3.0

Exercise B

Present counter-interpretations to the following:

  1. □(M→O),◊M⊨TO\Box(M\rightarrow O),\Diamond M\vDash_{\mathbf{T}}O

  2. □A⊨T□□A\Box A\vDash_{\mathbf{T}}\Box\Box A

3.0

Exercise C

Present counter-interpretations to the following:

  1. ◊A⊨S4□◊A\Diamond A\vDash_{\mathbf{S4}}\Box\Diamond A

  2. ◊A,□(◊A→B)⊨S4□B\Diamond A,\Box(\Diamond A\rightarrow B)\vDash_{\mathbf{S4}}\Box B

3.0
Properties of relationsNormal forms

Adapted from forall x: Calgary © 2025 P. D. Magnus, Tim Button, Robert Trueman, and Richard Zach. Licensed under CC BY 4.0. Source: forall x: Calgary. Imported at revision ec34df8.

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