It is impossible that Jason is thirsty. We doubt that Emily is a sheep. It is certain that Greg is yellow. Chances are about even that if 'Emily is a sheep and Jason is thirsty' then Brian is a frog. It is probably not the case that if either 'Emily is a sheep' or 'Jason is thirsty' but not both then Bernhard is a swan. There is a better than even chance that if 'Emily is a sheep' or 'Jason is thirsty' or both then Mary left the football.
It is probable that 'Brian is a frog' or 'Bernhard is a swan' or both.
It is highly unlikely that 'Brian is a frog' or 'Bernhard is a swan' or both.
It is probable that 'Brian is a frog' or 'Bernhard is a swan' or both.

  and(A,B) :- A,B.
  or(A,B) :- A;B.
  nand(A,B) :- not(and(A,B)).
  nor(A,B) :- not(or(A,B)).
  xor(A,B) :- or(A,B), nand(A,B).

  %hop0
  0.0::factA.
  0.2::factB.
  1.0::factC.
  %hop1
  0.5::factX:-and(factB,factA).
  0.25::factY:-xor(factB,factA).
  0.6::factZ:-or(factB,factA).

  %hop2
  conclusion:-or(factX,factY).

  query(conclusion).
  
'Brian is a frog' or 'Bernhard is a swan' or both.