Since C and D are conneted with
a zero resistor, they are equipotential.
Then superimpose C and D to obtain
the simplified circuit as shown. Since no
current flows in the branches CE and ED
cut and then thro them to have
`R_(AB) =R + R = 2R`
If we get a closed loop of resistors
without any battery, it carries no current
Then remove the total loop to get a
simpler circuit or if the current in any
branch is zero, remove it.
