True when expr is a positive integer power of 2:
abjad> from abjad.tools import mathtools
abjad> for n in range(10):
... print n, mathtools.is_positive_integer_power_of_two(n)
...
0 False
1 True
2 True
3 False
4 True
5 False
6 False
7 False
8 True
9 False
Otherwise false.
Return boolean.