Chances are slight that Greg is gray. It is highly unlikely that Lily is a frog. We doubt that Mary put down the milk. It is certain that if Lily is a frog, or Mary put down the milk, then Bernhard is white. We believe that if either Mary put down the milk, or Lily is a frog, then John went to the kitchen. There is a better than even chance that if Lily is a frog, or Mary put down the milk, then Brian is green.
It is unlikely that either Greg is gray, or Brian is green.
It is unlikely that either Greg is gray, or Brian is green.
It is probable that either Greg is gray, or Brian is green.
Either Greg is gray, or Brian is green.