how can source files see other files without path in a cmake project?

In a CMAKE project I have created 2 folders, a and b, each of which has include and src directories:

-- MyProject

CMakeLists.txt

---- a

------ include

-------- a.h

---- b

------ include

-------- b.h

...

a.h includes b.h. But only if the path is specified, ie, #include "../../b/include/b.h".

How can I configure cmake so that all project files can see each other without specifying the path? eg: #include "b.h"

via Chebli Mohamed