sorry, I have to correct you - you're wrong.
I shudder to think how you'd get gas in AND exhaust OUT with the same valve!
No, SOHC means that a single camshaft operates all the valves, and the inlet and exhaust valves are ALWAYS separate.
DOHC just means that there are 2 camshafts, one operating one set of valves, the other operating the second.