Trivedi sir, thanks f, it is indeed quite authoritative and answers a lot of questions.
As long as the 'lie' is intentional it is perjury. However innocent misrepresentations (lack of memory etc.) can be corrected immediately.
As per below, court may not find it expedient to prosecute just for 2 contradictory statements, but if it does, then it will result in conviction. But my question still remains - when these statements are made by 2 DIFFERENT witnesses.
Scenario: A says - "B is a family friend of A and is an eyewitness to a crime committed by C and is also a witness in this case". B says - " he is a family friend of A, but he is not an eye witness and has no idea about the crime at all". Clearly, one of them is lying. And logically speaking, it is A who is lying to strengthen his case against C. B being a friend of A, would not support C but also doesnt want to be a false witness.
Since the evidence of A and B has a direct bearing on C's fate, the contradiction must be handled. But how in this case ? (not just unable to prove, someone must take the responsibility for lying, otherwise its a miscarriage).
There are authorities, which will be mentioned later holding that when a witness admits having made a previous statement incorrectly and corrects himself later, it is not expedient to prosecute him for perjury. When, however, a witness makes two contradictory statements intentionally, there is nothing to show that the earlier statement was wrong and was corrected by the subsequent statement and he does not admit that he had committed a mistake in making the earlier statement and when the prosecution charges him in the alternative with making one of the two statements falsely, he must be convicted of perjury.