the local economy slows down, and decrease in activity if the local economy goes up. Disadvantages According to professor Nikolaus Läufer's theory, the use of local currencies such as Freigeld can only increase economic activity temporarily. Lengthy use of a local currency will ultimately result in a decline in economic activity and lead to a destabilization of the economy. This is due to the increased circulation velocity of the money as the amount in circulation decreases (as currencies as Freigeld reduce in value rapidly). Tax There are some complementary currencies that are regional or global, such as the Community Exchange System, WIR and Friendly Favors, Tibex in the Lazio region in Italy or the proposed global currency terra. A community currency is a type of complementary currency that has the explicit aim to support and build more equal, connected and sustainable societies. A community currency is designed to be used by a specific group. Since the advent of Bitcoin on January 3, 2009, cryptocurrency has increased substantially as an alternative currency. Cryptocurrency allows for a trustless means of exchange through the use of decentralized mining, in which computers solve mathematical puzzles first in order to verify the transaction. Activists Some complementary currency activists are Belgian ex-banker Bernard Lietaer, British economist Hazel Henderson, Dutch STRO-director Henk van Arkel that developed Cyclos, Qoin initiators Edgar Kampers and Rob van Hilten, Paul Glover of Ithaca HOURS, Margrit Kennedy from Monneta, LETSystem inventor Michael Linton, Time Banking inventor Edgar S. Cahn, Japanese Volunteer Labour Network founder Teruko Mizushima, Complementary Currency Resource Center coordinator Stephen DeMeulenaere and many others. Lietaer has argued that the world's national currencies are inadequate for the world's business needs, citing how 87 countries have experienced major currency crashes over a 20-year period, and arguing for complementary currencies as a way to protect against these problems. Lietaer has also spoken at an International Reciprocal Trade Association (IRTA) conference about barter. List of complementary currencies Other non-regional complementary currencies include: American Open Currency Standard (AOCS) Commercial credit circuit Community Exchange System (CES) – global exchange network Digital gold currency Fourth Corner Exchange Local Exchange Trading Systems (LETS) – an example of mutual credit, is a type of local currency used in a number of small communities worldwide. Rábaközi Tallér Sardex, alternative currency used in Sardinia Ven – a digital currency used in Hub Culture, a private social network WIR Bank – founded