To anyone who want to play a Arcane/Divine caster the Mystic Theurge class allows easily to build a character who at level 20 casts as a 17th level in one kind of magic and 13th in the other. With a simple trick it is possible enter the Mystic Theurge at level 5, but once you gained the 10 levels you still need to go up with the single classes as you cannot gain Epic levels before level 21.