Step 0: AddUp(1, 2, 3, 4)
Step 1: (1 + AddUp(2, 3, 4))
Step 2: (1 + (2 + AddUp(3, 4)))
Step 3: (1 + (2 + (3 + AddUp(4))))
Step 4: (1 + (2 + (3 + 4)))

--- Now with IndexBase = 1 ---
Step 1 of 5: AddUp(1, 2, 3, 4)
Step 2 of 5: (1 + AddUp(2, 3, 4))
Step 3 of 5: (1 + (2 + AddUp(3, 4)))
Step 4 of 5: (1 + (2 + (3 + AddUp(4))))
Step 5 of 5: (1 + (2 + (3 + 4)))