Explanation:

- Section 54: This section of the Indian Evidence Act specifies that in criminal cases, evidence of the accused's previous bad character is not relevant, except when such character has been introduced by the accused as an issue or in response to allegations.

- Section 59: This deals with proof of facts by oral evidence, meaning only statements that are spoken can be considered as oral evidence.

- Section 49: This section addresses the opinions as to usage, tenets, etc., when the court is required to form an opinion on them.

- Section 40: This section relates to the previous judgments relevant to bar a second suit or trial. It focuses on the finality of judgments in preventing re-litigation.