examples/simple/igraph_write_graph_lgl.out

Output without isolates:
# 0
1
2
# 1
2
3
# 2
4
# 3
4

Output with isolates:
# 0
1
2
# 1
2
3
# 2
4
# 3
4
# 5
# 6

Output vertex and edge labels:
# A
B 3
C 4
# B
C 5
D 6
# C
E 7
# D
E 8