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(Newbie question)

For every function I define I get this message:

enter image description here

When I close and reopen Mathematica, and re-enter the function definition, I don't get the message anymore. What does it mean?

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You can see that f is already defined because it's coloured black. You can verify this using ?f too. Instead of the drastic Remove[f] you can also use Clear[f] to clear all definitions, or f =. to remove f's value if f is a simple variable (in Mathematica terms: it only has OwnValues but not DownValues). –  Szabolcs Jun 13 '12 at 7:29
@Szabolcs - Thanks again. I should have known better than to use a single letter as a function or variable name :-/. But this was meant to be a quickie :-) –  stevenvh Jun 13 '12 at 7:31
You may find this discussion of some relevance. –  Leonid Shifrin Jun 13 '12 at 9:00

1 Answer 1

up vote 5 down vote accepted

It means you set f = 156 sometime before you executed that function definition. Executing a Remove[f] before your new definition should have fixed the problem.

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Thanks. Makes sense. But I also got this in a new notebook. Does that mean that the scope of symbols is session-wide instead of notebook-constrained? (Not what I would expect) –  stevenvh Jun 13 '12 at 7:19
Yes, session-wide. If you want to constrain your symbols to a particular notebook, see this question. –  J. M. Jun 13 '12 at 7:25
@stevenvh The kernel state is not specific to the notebook. You have to restart the kernel to clear its state completely. But if you want notebook-local symbols, you can use Evaluation -> Notebook's Default Context -> Unique to This Notebook. This option is available since version 6. –  Szabolcs Jun 13 '12 at 7:25
Thanks, J.M. and @Szabolcs. Szabolcs, I learned about it browsing through the list of SE sites at the top of another SE site's page. I'm mostly active in electronics.SE now, but registered in a dozen or so. –  stevenvh Jun 13 '12 at 7:30

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