For example, the 'closed system' is as described above.   But the 'open system' changes the paradox: on the front side of the card it is written, 'The statement on the backside of this card is true.' When the card is turned over, the back side says, 'The surface of the Earth is composed mostly of water.' Now there is a true statement, which results in eliminating the paradox.
  But now, the solution has very little resemblance to the original paradox.

Venn Diagrams

   What is a Venn diagram?
  "A diagram representing mathematical or logical sets pictorially as circles or closed curves within an enclosing rectangle (the universal set), common elements of the sets being represented by the areas of overlap among the circles."9

  What is the purpose of a Venn diagram?
  A Venn diagram clarifies the relationships of sets through comparison and contrast of the properties or of the elements of the sets.

  How are Venn diagrams constructed?
   Venn diagrams are a hierarchy extending from a universal statement downward to sets of elements with specific properties. It's similar to deductive reasoning analyzing from the general to the specific. And if you analyze in the opposite direction—from the specific to the general, then you will have inductive reasoning. (But you will never find this definition in any descriptions of Venn diagrams; at least, it has never been my experience to read one.)

  "A Venn diagram or set diagram is a diagram that shows all possible logical relations between a finite collection of different sets."10

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