use varieties of British, Australian and New Zealand Sign Language, unrelated to ASL. Similarly, the sign languages of Spain and Mexico are very different, despite Spanish being the national language in each country, and the sign language used in Bolivia is based on ASL rather than any sign language that is used in any other Spanish-speaking country. Variations also arise within a 'national' sign language which do not necessarily correspond to dialect differences in the national spoken language; rather, they can usually be correlated to the geographic location of residential schools for the deaf. International Sign, formerly known as Gestuno, is used mainly at international deaf events such as the Deaflympics and meetings of the World Federation of the Deaf. While recent studies claim that International Sign is a kind of a pidgin, they conclude that it is more complex than a typical pidgin and indeed is more like a full sign language. While the more commonly used term is International Sign, it is sometimes referred to as Gestuno, International Sign Pidgin or International Gesture (IG). International Sign is a term used by the World Federation of the Deaf and other international organisations. Linguistics In linguistic terms, sign languages are as rich and complex as any spoken language, despite the common misconception that they are not "real languages". Professional linguists have studied many sign languages and found that they exhibit the fundamental properties that exist in all languages. Such fundamental properties include duality of patterning and recursion. Duality of patterning means that languages are composed of smaller, meaningless units which can be combined into larger units with meaning (see below). The term recursion means that languages exhibit grammatical rules and the output of such a rule can be the input of the same rule. It is, for example, possible in sign languages to create subordinate clauses and a subordinate clause may contain another subordinate clause. Sign languages are not mime—in other words, signs are conventional, often arbitrary and do not necessarily have a visual relationship to their referent, much as most spoken language is not onomatopoeic. While iconicity is more systematic and widespread in sign languages than in spoken ones, the difference is not categorical. The visual modality allows the human preference for close connections between form and meaning, present but suppressed in spoken languages, to be more fully expressed. This does not mean that sign languages are a visual