• First-order logic is another way of knowledge representation in artificial intelligence. It is an extension to propositional logic.
• FOL is sufficiently expressive to represent the natural language statements in a concise way.
• First-order logic is also known as Predicate logic or First-order predicate logic. First-order logic is a powerful language that develops information about the objects in a more easy way and can also express the relationship between those objects.
• First-order logic (like natural language) does not only assume that the world contains facts like propositional logic but also assumes the following things in the world:
  • Objects: A, B, people, numbers, colors, wars, theories, squares, pits, wumpus, ……
  • Relations: It can be unary relation such as: red, round, is adjacent, or n-any relation such as: the sister of, brother of, has color, comes between
  • Function: Father of, best friend, third inning of, end of, ……

The notation is called BNF (for Backus-Naur Form).

Here, the symbols t, and α are meta-variables that range over terms and formulas,
respectively.

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