is this a mistake?

[busso]

so I'm reading a boot that demonstrates how logic gates work but these two examples don't make sense to me (they use relays instead of transistors)

1.

How Computers Work: Memory: Page 7

where power comes in at the bottom left corner, wouldn't just pressing switch b turn on light L? because it says In both b and a need to be switched on?
I wont bother with the next one now that I think of it, answering this would answer the other one

also I am referring to the top dagram on that page

[Ronald Roe]

Relay DB isn't connected to power unless DA is also closed. P0 is always hot, and A0 & B0 are only hot when the button is pressed. A0 and B0 apply power to their respective relay coils, pulling the arm down and closing the circuit. In the case of L, power must pass from P0 thru DA, into and thru DB to get to L.