Anchor: Three boys racing against each other on the track.
Entailed: Three people racing against each other on the track.
Contradiction: Three girls racing against each other on the track.
Contradiction: The man and the boy are playing basketball.
Contradiction: I doubt this approach has been followed well enough to be called a general rule.
Contradiction: The ice is so thick that merchants have no trouble fishing.  
Contradiction: The route of the tours may change from month to month, depending on what is being restored.