Anchor: Allowing for the possibility of increasing returns tends to rob economic models of two properties that economists  simplicity and determinism.
Entailed: It's possible to allow for increasing returns, but it robs economic models of two distinct properties.
Contradiction: There is no danger of robbing economic models of anything if you allow for increasing returns.
Contradiction: There's no need for a local boat trip in order to see them.
Contradiction: Some dogs running down a field.
Contradiction: A man walked over a bridge.
Contradiction: The man is posing