In (1), it's said that:
If two identical training symbols are transmitted consecutively, the corresponding signals with CFO of $\epsilon$ are related with each other as follows: $y_2[n]=y_1[n]\exp(j2\pi \epsilon)$.
How is this relation between $y_1[n]$ and $y_2[n]$ achieved? How is the exponential part associated with $y_1[n]$ obtained?
(1) Ishtiaq Akbar, A. Naveed Malik, "Performance analysis of carrier frequency offset estimation techniques for OFDM systems", Research journal of Applied Sciences, Engineering and Technology 6(11): 2041-2044, 2013