a=b change b a==b true??

[rstupplebeen at gmail.com]

I do not have a clue what is happening in the code below.

>>> a=[[2,4],[9,3]]
>>> b=a
>>> [map(list.sort,b)]
[[None, None]]
>>> b
[[2, 4], [3, 9]]
>>> a
[[2, 4], [3, 9]]

I want to make a copy of matrix a and then make changes to the
matrices separately.  I assume that I am missing a fundamental
concept.  Any help would be appreciated.

Rob Stupplebeen