Predicates and Variables

• Predicates are essential to logics.
• London is a City can be represented by City(London).
• You can think of Predicates as Functions.
• I can have multi-valued Predicates Taller(Chris,Ian).
• Instantiated Predicates have Truth Values:
  Taller(Chris, Ian) = True
  Taller(Ian, Chris) = False
• You can of course have variables
• Taller(x,Chris) refers to everyone who is Taller than Chris
• Note that all of the semantics in Taller are not part of the system, I might as well say Gern(x,Chris) or Gern(x,Ferb). Logic doesn't know anything about Taller unless you tell it.
• Also note that in Clips, predicates are done by placing the function as the first element in the brackets (Taller Chris Ian)