Your answer. YES.
You are correct.
10. Complex working is a requisite to duplex operation. If both operators send on the same
frequency at the same time, they will interfere with each other.
11. When transmission and reception between two stations is simultaneous, complex
frequencies are a must. This allows for a different frequency for each terminal to transmit on.
We stress this important fact - transmission and reception must be simultaneous for the
operation to be known as duplex. If it is not simultaneous, it is net duplex operation.