IUGG Symposium U4 `Non-Linear Dynamics and Predictability of Critical Geophysical Phenomena', 20 August 1991 Contents of folder inscribed `Gabrielov: Union Seminar U4': invitation, preliminary programme, typescript draft of paper by Lighthill 'The recently recognised failure of predictability in Newtonian dynamics' which he contributed to 1986 Royal Society/British Academy Discussion Meeting (see L/48-L/54). A. Gabrielov invited Lighthill to provide a general overview of non-linear science and chair the first session. 1991