the occurrence or non-occurrence of a credit event and rather leave the matter to the courts if necessary, though actual instances of specific events being disputed are relatively rare. CDS confirmations also specify the credit events that will give rise to payment obligations by the protection seller and delivery obligations by the protection buyer. Typical credit events include bankruptcy with respect to the reference entity and failure to pay with respect to its direct or guaranteed bond or loan debt. CDS written on North American investment grade corporate reference entities, European corporate reference entities and sovereigns generally also include restructuring as a credit event, whereas trades referencing North American high-yield corporate reference entities typically do not. Finally, standard CDS contracts specify deliverable obligation characteristics that limit the range of obligations that a protection buyer may deliver upon a credit event. Trading conventions for deliverable obligation characteristics vary for different markets and CDS contract types. Typical limitations include that deliverable debt be a bond or loan, that it have a maximum maturity of 30 years, that it not be subordinated, that it not be subject to transfer restrictions (other than Rule 144A), that it be of a standard currency and that it not be subject to some contingency before becoming due. The premium payments are generally quarterly, with maturity dates (and likewise premium payment dates) falling on March 20, June 20, September 20, and December 20. Due to the proximity to the IMM dates, which fall on the third Wednesday of these months, these CDS maturity dates are also referred to as "IMM dates". Credit default swap and sovereign debt crisis The European sovereign debt crisis resulted from a combination of complex factors, including the globalisation of finance; easy credit conditions during the 2002–2008 period that encouraged high-risk lending and borrowing practices; the 2007–2012 global financial crisis; international trade imbalances; real-estate bubbles that have since burst; the 2008–2012 global recession; fiscal policy choices related to government revenues and expenses; and approaches used by nations to bail out troubled banking industries and private bondholders, assuming private debt burdens or socialising losses. The Credit default swap market also reveals the beginning of the sovereign crisis. Since December 1, 2011 the European Parliament has banned naked Credit default swap (CDS) on the debt for sovereign nations. The definition of restructuring is quite technical but is essentially intended to respond to circumstances where a reference