Disallows using the same condition twice in an `if`/`else if` statement When you reuse a condition in an `if`/`else if` statement, the duplicate condition will never be reached (without unusual side-effects) meaning this is almost always a bug. ### Invalid: ```typescript if (a) {} else if (b) {} else if (a) {} // duplicate of condition above if (a === 5) {} else if (a === 6) {} else if (a === 5) {} // duplicate of condition above ``` ### Valid: ```typescript if (a) {} else if (b) {} else if (c) {} if (a === 5) {} else if (a === 6) {} else if (a === 7) {} ```