Question: Assignment problems

Hello clever people,

Here's an easy question for you all I'm sure (though as a novice I've been stuck on this for hours).

Why is it that when I'm using Maple 12 some of my assignments don't seem to work while others do? Most of the time I don't have a problem assigning matricies and vectors but quite often Maple doesn't seem to want to recall the contents of a variable when performing operations.

For example A and J are both 2*2 matricies that have previously been entered and manipulated without problems. Typing A displayes the A matrix but typing J displays only the letter J. Asking maple to evaluate A+J results in the letter J + the A matrix. I've attached an example.

Can someone please let me know what I'm doing wrong?

Many thanks,

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