Relation between prepayment invoices and "main" in

zutzu

Dynamics NAV 5.
I have an order.
I make two prepayment invoices for that order.
Afterwards, i invoice the order (i have the "main" invoice).
In the "main" invoice, the last line is the sum of the amount of the prepayment invoices (in negative).
In the invoice report, i need to show the number of the prepayment invoices.
Is there any relation between the prepayment invoices and the "main" invoice?