I just got off the phone with Singapore Consulate in San Francisco. The lady on the phone told me no visa required but you must have a valid 6 months RTD. However, they will not allow re-entry premit. It says it's not a valid travelling document. I'm a green card holder and recently applied for re-entry permit. My question is, can I use re-entry permit everywhere I go or only to few countries? or is it better to continously renew my RTD? which one is a better option?