JackFarmer

Tricky but it depends on context. If the narrative states that the information "was" relayed to a listener then you treat everything that the narrator said with a past tense. If the narrator of the story is speaking directly to the listener, then "shown to be" or "proves to be" is probably best.

Thanks, nbohr, however, the question was meant more philosophically (even if I expressed it pointing to the grammar) in view of the fact that when you talk about science fiction books, you talk about the action in the past....although it will only happen in the distant future!