How to mix multiple Enviroment texture (not in the compositing) If i want to join 2 different HDR called A &amp; B. I want to create a new Enviroment whith 180° of "A" and other part of "B". I don't want to use the compositing because i need the real effects of the 2 enviroment. 

There is a genius of nodes able to do this? 

Thak you!
No need to be a genius. Just mix it with a mask:



As you can see you can use a radial gradient clamped at some value with a color ramp, but image texture masks would work as well.