Question: What's the name of the agreement allowing free passage across northern European borders including the one between Finland and Sweden?

<P0-S0> The Nordic Passport Union allows citizens of the Nordic countriesIceland, Denmark, Norway, Sweden, and Finlandto travel and reside in another Nordic country (excluding Greenland and Svalbard) without any travel documentation (e.g. a passport or national identity card) or a residence permit. <P0-S1>  Since 25 March 2001, all five states have also been within the Schengen Area. <P0-S2>  The Faroe Islands are part of the Nordic Passport Union but not the Schengen Area, while Greenland and Svalbard are outside both. <SEP> <P1-S0> The Finnish-Swedish border is the border between the countries of Finland and Sweden. <P1-S1>  Almost the entire border runs through water: along the Tornio River and its tributaries, and in the Gulf of Bothnia. <P1-S2>  Only a few kilometres of the border are on dry land. <P1-S3>  Because of the Schengen treaty and the Nordic Passport Union, the border can be crossed mostly freely. <SEP> <P2-S0> 2013 Nordic storms were a series of storms affecting predominantly the Nordic nations with other northern European nations also affected. <P2-S1>  The first storm in the series Hilde, named Otto by Free University of Berlin, and Eino in Finland was an extratropical cyclone affecting parts of northern Europe, causing disruption to electricity supplies and transportation across mid Norway, northern Sweden and central Finland in 15. <P2-S2>  – 18. <P2-S3>  November 2013. <P2-S4>  The storm brought a new record average wind speed to Sweden (at altitude), however wind speeds at lower altitudes were less than seen during the Dagmar storm of 2011. <P2-S5>  Most damage was caused by falling trees along the storms path likely exacerbated by unfrozen ground. <P2-S6>  The total cost of damage is likely to be low, as the storm passed over relatively unpopulated regions of the Nordic nations. <SEP> <P3-S0> Swedish neutrality refers to Sweden's former policy of neutrality in armed conflicts, which was in effect from the early 19th century, until 2009, when Sweden entered into various mutual defence treaties with the EU, and other Nordic countries. <P3-S1>  In 2016 Sweden became a "NATO Affiliate" (not member), and signed a treaty allowing NATO operations to take place within the country's borders. <P3-S2>  Sweden's previous neutrality policy had originated largely as a result of Sweden's involvement in the Napoleonic Wars during which over a third of the country's territory was lost, including the traumatic loss of Finland to Russia. <P3-S3>  Resentment towards the old king precipitated a "coup d'état" and the new regime formulated a new foreign policy which became known as "The Policy of 1812". <P3-S4>  Since the time of the Napoleonic Wars, Sweden has not initiated any direct armed combat. <P3-S5>  However, Sweden's military and government have been involved in major peacekeeping actions and other military support functions around the world. <P3-S6>  The accession to the European Union in 1995 meant that neutrality as a principle was abolished. <P3-S7>  Sweden is still today a neutral and non-aligned country in regard to foreign and security policy. <P3-S8>  However, it maintains strong links to NATO.