We doubt that John is in the garden. Chances are about even that Julius is a lion. We believe that Mary picked up the milk. It is impossible that if 'Mary picked up the milk and John is in the garden' then Jessica is a mouse. There is a better than even chance that if either 'John is in the garden' or 'Julius is a lion' but not both then Bernhard is a frog. It is highly unlikely that if 'John is in the garden and Julius is a lion' then Greg is a rhino.
We believe that 'Jessica is a mouse and Greg is a rhino'.
It is impossible that 'Jessica is a mouse and Greg is a rhino'.
We believe that 'Jessica is a mouse and Greg is a rhino'.

  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
  0.2::factA.
  0.5::factB.
  0.75::factC.
  %hop1
  0.0::factX:-and(factC,factA).
  0.6::factY:-xor(factA,factB).
  0.05::factZ:-and(factA,factB).

  %hop2
  conclusion:-and(factX,factZ).

  query(conclusion).
  
'Jessica is a mouse and Greg is a rhino'.