Rules allowing or requiring witnesses not to testify in certain kinds of trials or proceedings or allowing or requiring witnesses in trials or proceedings not to disclose information about certain types of matters

Fed. R. Evid. 415(b) ("A party who intends to offer evidence under this Rule shall disclose the evidence to the party against whom it will be offered, including statements of witnesses or a summary of the substance of any testimony that is expected to be offered, at least fifteen days before the scheduled date of trial or at such later...In a case in which a party intends to offer evidence of other sexual wrongs under a rule such as Federal Rule of Evidence 415 or a comparable State rule, the offering party may be required to disclose such evidence in advance to the party against whom such evidence will be offered.

Fed. R. Evid. 804(a)(3) (declarant is unavailable if declarant "(3) testifies to a lack of memory of the subject matter of the declarant's statement").For purposes of the hearsay exceptions created by Federal Rule of Evidence 804 or a comparable State rule, a declarant is "unavailable" within the meaning of Rule 804(a) or a comparable State rule if the declarant testifies to a lack of memory of the subject matter of the declarant's statement; but a declarant is not "unavailable" if such claim of lack of memory is due to the procurement or wrongdoing of the proponent of a statement for the purpose of preventing the witness from attending or testifying.

United States v. Ross, 92 U.S. 281, pin? (1875) (Court rejected the the claimant's attempts to trace the bales of cotton from capture to sale: "These seem to us to be nothing more than conjectures. They are not legitimate inferences, even to establish a fact; much less are...Inferences on inferences are impermissible