Why Are the 5 and 20 Ohm Resistors in Parallel?

[princejan7]

I'm trying to find the equivalent resistance of this circuit but I don't know where to start.

The solution manual says that the 5 and 20 ohm resistors are in parallel as well as the 6 and 3 ohm resistors. Can someone explain why?

 

[BvU]

Go from a to b: after 10 ohm you can turn up or down and end up at one and the same voltage (the wire that runs around to the left) Again you can go via 6 or 3 and the final hurdle is the 8 ohm.
Now draw the picture again, with a at the top and b at the bottom.