Question: How do I unprotect "I" to use it in equations?

"I" is reserved for square root of -1.  I don't use complex numbers and want to use "I" in my equations.  How do I go about doing this?  I tried to unprotect it with a number of variations of quoting "I".

I'm using document mode with Maple 13 on Apple.

Thanks for your help.

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