Combining Texts

You have chosen 'The Sign of Four' by Arthur Conan Doyle, 'A Specimen of Discoveries' by Gottfried Leibniz and 'The Problem of Natural Laws' by L. Jonathan Cohen

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All the ideas for Existence, or select a subheading:
      A. Nature of Existence
      B. Change in Existence
      C. Structure of Existence
      D. Theories of Reality
      E. Categories