Anchor: The theory that only a monopolist can price discriminate is standard textbook fare, and it's borne out by a lot of observations.
Entailed: The monopolist theory stems from many observations.
Contradiction: The theory doesn't exist, it's a figment of the imagination.
Contradiction: A platform held the fire.
Contradiction: Two girls are sitting down by the river.
Contradiction: This approach is never used because engineers hate it.
Contradiction: people are selling stuff