Example 1.
Create a pair of manifolds.
The command DGinfo can return a list of all defined manifolds, adapted frames, Lie algebras, etc. - everything created by DGsetup.
Note that u is protected and D_u is assigned.
_DG([["vector", N, []], [[[1], 1]]])
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Now remove the frame N.
The frame N no longer shows up in the list of defined frames.
The current frame is now M.
Also, u is no longer protected and D_u is unassigned.