Combining Texts

You have chosen 'The Value of Science' by Henri Poincaré, 'On the General Idea of Proof Theory' by Dag Prawitz and 'The Art of the Infinite' by R Kaplan / E Kaplan

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All the ideas for Modality, or select a subheading:
      A. Necessity
      B. Possibility
      C. Sources of Modality
      D. Knowledge of Modality
      E. Possible worlds