Anchor: To be sure, people who have to switch HMOs may have to change doctors.
Entailed: Changing HMOs may result in having to switch doctors.
Contradiction: No one who has changed their HMO has ever had to switch doctors.
Contradiction: I have been cautious enough.
Contradiction: The buiding has been a house and then a jail.
Contradiction: I've never thought of that before, Kirby, admitted Shannon. 
Contradiction: An old man is sitting.