functions, list, default parameters

[Mark Wooding]

Lawrence D'Oliveiro <ldo at geek-central.gen.new_zealand> writes:

> In message <mailman.608.1288889032.2218.python-list at python.org>, Robert Kern 
> wrote:
> > So examining LHS "selectors" is not sufficient for determining
> > immutability.
>
> Yes it is. All your attempts at counterexamples showed is that it is not 
> necessary, not that it is not sufficient.

You've got them the wrong way around.  A is sufficient for B if and only
if B is true whenever A is true; i.e., it is never the case that A is
true and B is false.  In this case, we also say that B is necessary for
A.

See also http://en.wikipedia.org/wiki/Necessary_and_sufficient_condition

-- [mdw]