<｜begin▁of▁sentence｜>### Instruction:
Given a multi-graph with nodes 1, 2, and 3, where nodes 1 and 2 are connected by two parallel edges, and each node 1 and 2 is connected to node 3 by a single edge, what is the volume of the set S = {1, 2}?
### Response:
import networkx as nx

# Create a Graph
G = nx.MultiGraph()

# Add nodes
G.add_node(1)
G.add_node(2)
G.add_node(3)

# Add edges
G.add_edge(1, 2)
G.add_edge(1, 3)
G.add_edge(2, 3)
G.add_edge(1, 2)  # parallel edge

# Define the set of nodes S
S = {1, 2}

# Calculate the volume of set S
vol = nx.volume(G, S, weight='weight')

print('The volume of set S:', vol)
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