source	target	weight
A	B	1
A	C	1
B	C	1
A	D	1
D	E	1
D	F	1
E	F	1
A	G	1
D	G	1
G	H	1
G	I	1
H	I	1
C	J	1
J	L	1
J	K	1
K	L	1