Chances are slight that John went to the garden. It is certain that Gertrude is a mouse. There is a very good chance that Bernhard is a swan. It is probably not the case that if 'Bernhard is a swan and John went to the garden' then Sandra dropped the milk. There is a very good chance that if either 'John went to the garden' or 'Gertrude is a mouse' but not both then Brian is a rhino. Chances are about even that if 'Gertrude is a mouse and John went to the garden' then Greg is a lion.
It is highly likely that 'Brian is a rhino and John went to the garden'.
It is impossible that 'Brian is a rhino and John went to the garden'.
It is highly likely that 'Brian is a rhino and John went to the garden'.

  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
  0.1::factA.
  1.0::factB.
  0.8::factC.
  %hop1
  0.25::factX:-and(factC,factA).
  0.8::factY:-xor(factA,factB).
  0.5::factZ:-and(factB,factA).

  %hop2
  conclusion:-and(factY,factA).

  query(conclusion).
  
'Brian is a rhino and John went to the garden'.