Text: I'm not sure if the correspondents realize that the Hindu concept of Brahman has been around considerably longer than Sullivan's cross-pollination of something like the  a powerful (yet devout) bearded man, a cool breeze on a clear summer night, a John Lennon tune, and the Lion King.
Entailment: I'm not sure that the current correspondence realize that the Hindu concept of Brahman has been around.
Contradiction: I am totally sure that the correspondence realize that the Hindu concept has been around.