Fixing a typo -- thanks, Bjorn!

If md5sha1sum is not installed the following error will be thrown:

/bin/sh: md5sum: command not found
Traceback (most recent call last):
  File "test.py", line 118, in <module>
    d = compute_checksums(dirname='.', suffix='.py')
  File "test.py", line 77, in compute_checksums
    res, stat = compute_checksum(name)
  File "test.py", line 37, in compute_checksum
    return pipe(cmd)
  File "test.py", line 62, in pipe
    assert stat is None
AssertionError

The solution is to install it on the operating system

Adding a note for more clarity

Took the "factor" term outside the braket of infinite summation so that they all have to be added only once

Update pi.py

Adding glossaries compiled by Peter Hall