At left is a sequence of recursive calls, starting at bottom left and moving up in a column. Arrows indicate the flow from bottom to top, as follows:

power(2, 3)

power(2, 2)

power(2, 1)

power(2, 0)

Each of these is within an oval, and each of the last 3 ovals is nested in a larger oval containing the expression “*2”. An arrow points from the power(2, 0) oval to the number 1 at top.

The sequence continues at right in a column from top to bottom, showing how the final value is computed. An arrow points from the number 1 at top to the sequence 1, 2, 4, 8 from top to bottom, with an arrow pointing from each number to the next. Each of the numbers is within an oval, and each of the “1”, “2”, and “4” ovals is nested in a larger oval containing the expression “*2”. The last 3 arrows are labeled “1*2 is 2”, “2*2 is 4”, and “4*2 is 8”, respectively. At bottom is the statement “power(2, 3) is 8”.