The call = put fly, but I usually structure the natural with the body otm as opposed to going with the put natural in this case. Microstructure will always favor the combo (iron fly in red).
Below, the iron fly mid is only a nickel off NBBO bid while the natural's mid below is 15 cents off the ask.
The iron fly is equivalent to the natural as the 71/81 short put vert is equivalent to the natural's 71/81 long call vert (box arbitrage). Further, you can see below that the natural debit of 3.96 risk equates to the synthetic credit of 6.07 (3.93 risk).
Below, the iron fly mid is only a nickel off NBBO bid while the natural's mid below is 15 cents off the ask.
The iron fly is equivalent to the natural as the 71/81 short put vert is equivalent to the natural's 71/81 long call vert (box arbitrage). Further, you can see below that the natural debit of 3.96 risk equates to the synthetic credit of 6.07 (3.93 risk).
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