Once a teacher, always a teacher. And proof of that - Finance Minister Pranab Mukherjee. Some 40 years ago, he used to teach political science at a college in suburban Kolkata. Yesterday, Professor Pranab was back in an unusual classroom: the West Bengal Assembly. His students no less unusual: 42 Congress MLAs - 23 of them first timers. Their lesson: how to conduct themselves in the upcoming session of the House.