Market maker schemes are designed to provide visible liquidity in the contracts they operate in. The effect of a corporate event on futures and options contracts depends on the specific nature of each event. This may be achieved by changing any or all of the price, lot size or the deliverable asset. Generally futures and options are adjusted for special dividends, but not for ordinary dividends. Also, index futures and options are not adjusted to reflect corporate events, but in some cases, the index calculation may be adjusted.
Open interest refers to the number of outstanding contracts that remain open.
If however the trader decided to close out their position, the open interest for that contract would decrease. There are two major types of margin - initial and variation. Initial margin is a deposit required on all positions and is returned by the clearing house when positions are closed. It protects the LCH from any adverse price movements in the event of a clearing member defaulting. Variation margin reflects the change in value of a portfolio of contracts and is calculated and paid daily.