Anchor: The dramatically rising cliff of black basalt stone made the castle impregnable to all but the most wily commander.
Entailed: The castle was secure due to its proximity to a cliff.
Contradiction: The castle could be easily invaded by almost anyone. 
Contradiction: You shouldn't bother asking the dealer for an invoice. 
Contradiction: A cheerleader holds a girl in the air.
Contradiction: A rollerblader races on an indoor track.
Contradiction: There are two tricky questions, one of which is what are the fringe issues on which differences are not crucial.