how to check spatial references for layers and map doc matching in code

Hi, is there any way (in code) to check matching spatial references between layers against map document? If I have a set of layers / feature classes in an MXD ... how to check each one of them matches the map spatial reference in code?

What does IProjectedCoordinateSystem2.IsEqualNoNames really do? Is there something similar for geographic coordinate system?

Thanks. :confused: