4:28 God, isn' it false ? Shouldn't it be  x = 1 and y = 2 ? Y is okay but x = -1 doesn't seem correct####[['NULL', 'Mathematical_Related_Concept', 'NEU'], ['NULL', 'Mathematical_Related_Concept', 'NEU'], ['NULL', 'Mathematical_Related_Concept', 'NEU'], ['NULL', 'Mathematical_Related_Concept', 'NEU']]