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In this example the Ace in your hand also appears on the board. You must therefore use the Six and Four as the two cards from your hand to make a Seven-low of 7-6-4-2-A. It doesn't matter that your five low cards are all the same suit. Flushes are ignored for the purposes of calculating low hands.

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Unfortunately, you don't have a low here at all. You don't have five cards that can make a low between them. Only four, which is worthless. Both the Ace and Four from your hand are duplicated on the board.