1. A method of planning tasks in a machine, the machine being at least a sub-system of a lithographic apparatus or lithographic processing cell, the method comprising: receiving an order for work to be carried out by the machine; determining key tasks to be carried out to fulfill the order; generating a key task sequence comprising the key tasks; determining any subsidiary tasks, including one or more logistic tasks, one or more pre-processing tasks and/or one or more post-processing tasks, to be carried out before or after each of the key tasks; and generating a scheduling problem instance comprising the subsidiary tasks linked to respective ones of the key tasks.