This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
Multidimensional arrays are nothing more than arrays of arrays, and an array is in the end still an object. Therefore, you merely have another reference to the same array object. So yes, it points to a1 and nothing is copied.