Section 241.1. Perjury.

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 (3) Irregularities No Defense.  It is not a defense to prosecution under this Section that the oath or affirmation was administered or taken in an irregular manner or that the declarant was not competent to make the statement.  A document purporting to be made upon oath or affirmation at any time when the actor presents it as being so verified shall be deemed to have been duly sworn or affirmed.

 (4) Retraction.  No person shall be guilty of an offense under this Section if he retracted the falsification in the course of the proceeding in which it was made before it became manifest that the falsification was or would be exposed and before the falsification substantially affected the proceeding.

 (5) Inconsistent Statements.  Where the defendant made inconsistent statements under oath or equivalent affirmation, both having been made within the period of the statute of limitations, the prosecution may proceed by setting forth the inconsistent statements in a single count alleging in the alternative that one or the other was false and not believed by the defendant.  In such case it shall not be necessary for the prosecution to prove which statement was false but only that one or the other was false and not believed by the defendant to be true.

 (6) Corroboration.  No person shall be convicted of an offense under this Section where proof of falsity rests solely upon contradiction by testimony of a single person other than the defendant.