What is the relationship between the Aztec and Inca Empires?

I've been reading about the empires of Central and South America prior to Spanish conquest in the 16th century. I'm not aware of the existence of any notable events or circumstances where these two powers interacted with one another. <br><br>I'm curious to know if there were any diplomatic or military relations between them, or if they were aware of each other in any way. What were the borders of their influence? Were there any trade relations between them?