5 ========================================
6 Define the groups on the model of blocks
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9 A group is characterized by the three following components:
15 The six following classes define all the kind of group:
17 - group3d for groups of hexahedra,
18 - group2d for groups of facets,
19 - group1d for groups of segments,
20 - group0dVertices for groups of nodes on the edges,
21 - group0dFaces for groups of of nodes on the faces,
22 - group0dBlocks for groups of nodes in the blocks,
24 See TUI scripts and GUI part.