It was found that the standard Glass shader and Principled BDSF shader of Blender has the drawback of making objects behind the glass material appeared too dark. Some people has devised work-around by using the following shaders.
But there is a problem. Besides the expected reflection image, a faint redundant "ghost reflection" appears between the glass surface and reflection image. It's location depends on the glass shader's IOR value.
How can we remove this "ghost reflection"?