If worker 1 can perform service A (with 3 slots) or service B (with 6 slots). If someone books worker 1 with service A at time slot X then you should not be able to book worker 1 - service B because worker 1 is now busy with service A. However, it seems worker 1 could end up with 9 appointments, rather than just 3 if A is booked first or 6 if B is booked first)