There is no reason yet to think that this is a double spend attempt.
The person that sent you the transaction included bitcoins that they received from a transaction that has not yet confirmed. You should contact the sender and inform them that they should not use unconfirmed bitcoins when funding a transaction. If their wallet did this without their control, then you should inform them that they should switch to a wallet that does not do this. You should refuse to engage in transactions with them in the future unless/until they inform you that they have taken the necessary steps to avoid spending unconfirmed bitcoins.
It is
quite likely that both their transaction and yours will confirm soon (within the next few hours), but there is a small possibility that one (or both) transactions are dropped from memory pools before they confirm.
You should wait for at least 1 confirmation before you consider this transaction to be safely completed.I've posted the raw transactions below in case they are dropped from the memory pools and you (or anyone else) wants to re-broadcast them:
The transaction that you received:
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
The unconfirmed transaction that was used to fund the transaction to you:
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
