<｜begin▁of▁sentence｜>### Instruction:
Given a graph with certain connectivity properties, can you use the CohesiveBlocks.CohesiveBlocks.parent function in igraph to determine the parent group index of a given cohesive group within the graph structure?
### Response:
from igraph import Graph, CohesiveBlocks

# Create a simple undirected graph
graph = Graph.Formula('A--B--C--D--A--C, A--D, B--D')

# Initialize the cohesive blocks structure
cblocks = CohesiveBlocks(graph)
cblocks = cblocks.calculate()

# Get the parent group index of a given group
parent_index = cblocks.parent(2)

# Print the parent index of group 2
print('Parent index of group 2:', parent_index)
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