event number one is the instant t equal to zero when the left end of the ladder enters the garage and notice that as anticipated because i made this point which we know is l root one - v^2 over c^2 less than g then there, the entire ladder at this point is enclosed in the garage and this goes on until the time of this event labelled two, event number two is the instant where the right end of the ladder starts protruding from the garage and so as i suggested there, there is this whole region here from t1 to t2 where the entire ladder's inside the garage, okay?