Anchor: Until the advent of Christianity, Samothrakiawas a very important island indeed.
Entailed: Samothrakia was an island of high importance before Christianity began.
Contradiction: Samothrakia was never an island of any importance.
Contradiction: Sounds perfectly rational to me.
Contradiction: A skiier is on snow.
Contradiction: The weather was beautiful and calm everywhere.
Contradiction: Dr Elkbellows invented a series of exercises.