Six managers of Muddle and Company have to schedule a series of meetings on various aspects of the company's activities. Not all of them are to attend every meeting, but each of them has to attend three or four meetings. The managers' names are Amy, Bernard, Chester, Dianne, Emma and Frank. The meetings concern marketing, networks, orders, production, quality control, revenue, sales and timetables. These may take place in any order, except that the meeting on sales must happen before the one on marketing, and both production and quality control have to be discussed before the timetabling meeting can take place. The meetings they are required to attend are:

They want to schedule the meetings to fit into the smallest possible number of timeslots, so as to get to their golf game straight after lunch. They find it hard to decide how many timeslots they need and which meetings to hold in parallel with which.

Can you help them out?