Maximum-efficiency conjecture for practical multi-user OFDM systems

Let a practical multi-user OFDM system have $K$ users and $N$ subcarriers, with the number of subcarriers less than $2{,}002$, and let $d_{\max}$ denote its maximum efficiency.

Maximum-efficiency conjecture. The maximum efficiency is $d_{\max}=1.4998$, achieved when there are $K=3$ users using $N=2{,}001$ subcarriers.

This statement identifies the best efficiency found by the paper's analysis for practical systems subject to the stated subcarrier limit. The source does not provide evidence that the claim has been proved or disproved.