<s>
In	O
graph	O
theory	O
,	O
a	O
nowhere-zero	B-Algorithm
flow	I-Algorithm
or	O
NZ	O
flow	O
is	O
a	O
network	B-Algorithm
flow	I-Algorithm
that	O
is	O
nowhere	O
zero	O
.	O
</s>
<s>
If	O
φ(e )	O
≠	O
0	O
for	O
every	O
e	O
∈	O
E	O
,	O
we	O
call	O
φ	O
a	O
nowhere-zero	B-Algorithm
flow	I-Algorithm
,	O
an	O
M-flow	O
,	O
or	O
an	O
NZ-flow	O
.	O
</s>
<s>
Modify	O
a	O
nowhere-zero	B-Algorithm
flow	I-Algorithm
φ	O
on	O
a	O
graph	O
G	O
by	O
choosing	O
an	O
edge	O
e	O
,	O
reversing	O
it	O
,	O
and	O
then	O
replacing	O
φ(e )	O
with	O
−	O
φ(e )	O
.	O
</s>
<s>
After	O
this	O
adjustment	O
,	O
φ	O
is	O
still	O
a	O
nowhere-zero	B-Algorithm
flow	I-Algorithm
.	O
</s>
