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Keep your XEM in your XEM wallet until the time of snapshot to receive free XYM at Symbol launch.
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This point is not covered in detail, it needs detailing. Although, there was an explanation:
I understand that only the funds in my account on the snapshot block are the funds that will be included in my XYM account balance at Symbol launch. Any account balance changes after this opt transaction but before the snapshot will be reflected at Symbol launch.
So, the Opt-in (subscription, registration) before the snapshot makes an application for an account in the Symbol genesis block, with the funds that will be in the corresponding NEM account at the time of the snapshot; the snapshot will take place in December. To participate in the Opt-in, a NEM account must have at least 100 XEM. After the Opt-in has taken place, the funds on this NEM account do not need to be fixed before the snapshot. During this period, you can make any free movement of funds on it - reduce, increase and even zero funds. It is only important that at the time of the snapshot there is the necessary or possible amount on this account.
Example #1.The account now has 100 XEM and it has passed the Opt-in. At the time of the snapshot, 100k XEM has accumulated there. Result: 100k XYM will be fixed on the Symbol account.
Example #2.Now the account has 100k XEM and it has passed the Opt-in. But at the time of the snapshot there are 100 XEM left. Result: 100 XYM will be fixed on the Symbol account.
Example #3.The account did not participate in the Opt-in, but at the time of the snapshot there were 1000 XEM. For 6 years after the snapshot, the account holder can claim 1000 XYM on the Symbol network.