choose all identical shapes in two layers in divaDRC.rul DRC

[Jie]

I am trying to get a derived layer in DIVA DRC.rul file by the
following request:
There are two layers "layer1" and "layer2". Shapes in "layer2", which
may overlap each other, should treated as different shapes. I want to
find the areas where two shapes in "layer1" and "layer2" are
identical. And save all the identical shapes to a derived layer
"Layer1Layer2Same".

What I have done is as following:
layer1 = geomOr("layer1")
(Layer1InsideLayer2 = geomInside(layer1 "layer2"))
(Layer2InsideLayer1 = geomInside("layer2" layer1))
(Layer1Layer2Same = geomAnd(Layer1InsideLayer2 Layer2InsideLayer1))

However, once two shapes (shape1, shape2) in "layer2" overlap each
other, even though shape1 is identical to a shape (shape3) in
"layer1", it is not included in the derived layer "Layer1Layer2Same".
Or more specifically, it is not included in the derived layer
"Layer2InsideLayer1", I guess because cadence merged shape1 and
shape2.

Any one can help me on this issue? Thanks!

Jren