Formal logic language

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Introduction

Formal logic plays an important role, especially so in set theory, but overall an important role. It is important to have a concrete understanding of this.

Example 1

xyz((P(x,y)P(y,z))P(x,z))
xyz(P(x,y)P(y,z)P(x,z))
  • for all x
  • for all y
  • for all z
  • if
    • we have
      • both
        • P(x,y)
        • P(y,z)
    • then
      • P(x,z)
  • for all x
  • for all y
  • for all z
  • we have both
    • P(x,y)
    • if
      • we have
        • P(y,z)
      • then
        • P(x,z)
Whenever we have (P(x,y) and P(y,z)) we also have P(x,z) P(x,y) is true and whenever P(y,z) is true then P(x,z) is true
It is always true that if (P(x,y) and P(y,z)) then P(x,z) It is always true that P(x,y)) and (if P(y,z) then P(x,z))
P(x,y) P(y,z) P(x,z)
Uncertain
True Uncertain
True Uncertain
True True True
P(x,y) P(y,z) P(x,z)
True (definition) Uncertain
True (definition) True True