I saw this phase many times but I don't know exactly what it exactly mean. Is there anybody to tell me about this and examples are welcome as well. Many thanks.
Zhi
I saw this phase many times but I don't know exactly what it exactly mean. Is there anybody to tell me about this and examples are welcome as well. Many thanks.

"Not unless" = "only if".

Jim Heckman
Jim Heckman, thanks for your response.