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#### Merge

The `union` operation just glues objects together, it does not remove the objects' surfaces inside the `union`. Under most circumstances this doesn't matter. However if a transparent `union` is used, those interior surfaces will be visible. The `merge` operations can be used to avoid this problem. It works just like `union` but it eliminates the inner surfaces like shown in the figure below.

Merge removes inner surfaces.

The syntax is:

MERGE:
`
  merge {
` SOLID_OBJECTS... [OBJECT_MODIFIERS...] `}`

The component objects must have well defined inside/outside properties. Patch objects are not allowed. Note that `merge` is slower rendering than `union` so it should only be used when it is really necessary.

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