Nadia titled her head, "The addition, not the subtraction?" she blurted mechanically but kept listening. She made a mental note about the non-existance of negative numbers. But that last question might not be completely useless.

"Professor," she raised her hand again, "You say it's possible to use the four basic arithmetic operations. I was thinking the addition of two spells would be mixing them, like, send the two spells at the same time into one hex. If that would be the "addition" of spells, which would be the subtraction? And how about multiplication or divition of spells?"