hi method, Open Interest is the number of contracts that have been bought, but no exercised. In otherwords, if you were to buy 100 Call contracts at the 36 strike, that would be added to the total Open Interest.
When you sell those call (i.e. take profit), that 100 will be subtracted from the total OI.
if the OI on the 35 puts have decreased, it likely means some of that may be due to profit taking or that some are removing their hedge from the table.
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