Q for code

[xueleecs]

# 2
# Keep the proteins involved
proteinID1 = [Po_pairs[i][0] for i in range(len(Po_pairs))]
proteinID2 = [Po_pairs[i][1] for i in range(len(Po_pairs))]
proteinID3 = [Ne_pairs[i][0] for i in range(len(Ne_pairs))]
proteinID4 = [Ne_pairs[i][1] for i in range(len(Ne_pairs))]
proteinID = list(set(proteinID1 + proteinID2 + proteinID3 + proteinID4))
add_nodes = list(set(proteinID3 + proteinID4) - set(proteinID1 + proteinID1))  ##

In SGAD.py,line 477 (the last line above), "proteinID1 + proteinID1", Why use "proteinID1" twice, and use "proteinID1" once is also the same result. Would you please take the time to answer my questions