The configuration indicated by the green circle is adjacent to all configurations at its boundary (red and blue regions in Fig. ). For a bounded region as this example is, it follows that all transformations within the 2D region and onto its boundary configurations must all have the same symmetry, here denoted 𝑠 𝑘,1 , with this being a Mulliken symbol in the character table for "PG1". Regions with different topologies can demonstrate more complex transformation symmetries (see Section 3.3).