yes it is. The rule says percussion as required. As the part was written for 3 and we wanted to play 4 I emailed Kapitol to clarify the meaning of this and the reply I got was that it was the amount of percussionists the conductor requires not the amount of parts written.There would be no problem with us playing 4 I do intend taking a printed copy of this with me on Sunday just in case there are any problems