We use several price lists in odoo. 

Customers can get fixed price for some products. 
Those products are different for all customers. Therefor, those prices are in a special customer price list connected to the customer.

For an example: Customer AA has his specific price list "Price Customer AA"

We also have a 40% discount list for various products we can give to a customer. 
How can I implement this 40% in the specific "Price Customer AA" price list.

I've tried to make an extra price list item (formula) based on another price list: "40% discount".
 Then the customer specific price list is overruled by the 40% and the fixed prices are not used.
Is there a specific order how the discounts are used? How can i use several price lists at the same time for one customer?