Relation pm#probability_relation__probabilityrelation (formula,?)
  supertype:  relation_from_description
  instance of:  probability_relation_type
  subtype:  probability_fn__probabilityfn (formula -> real_number)  one of the basic probability_relations, probability_fn is used to state the a priori probability of a state of affairs represented by the given formula
  subtype:  conditional_probability__conditionalprobability (formula,formula,real_number)  the probability of 'the 2nd formula being true given that the 1st formula is true' is the number given as 3rd parameter
  subtype:  increases_likelihood__increaseslikelihood__increases_likelihood_of (formula,formula)  the 2nd formula is more likely to be true if the 1st is true
  subtype:  decreases_likelihood__decreaseslikelihood__decreases_likelihood_of (formula,formula)  the 2nd formula is less likely to be true if the 1st is true
  subtype:  independent_probability__independentprobability (formula,formula)  the probabilities of the formulas being true are independent