50) programming languages) Web application → C (web application source code consists of HTML, JavaScript, and CSS) Multiquines David Madore, creator of Unlambda, describes multiquines as follows: "A multiquine is a set of r different programs (in r different languages – without this condition we could take them all equal to a single quine), each of which is able to print any of the r programs (including itself) according to the command line argument it is passed. (Cheating is not allowed: the command line arguments must not be too long – passing the full text of a program is considered cheating)." A multiquine consisting of 2 languages (or biquine) would be a program which: When run, is a quine in language X. When supplied with a user-defined command line argument, would print a second program in language Y. Given the second program in language Y, when run normally, would also be a quine in language Y. Given the second program in language Y, and supplied with a user-defined command line argument, would produce the original program in language X. A biquine could then be seen as a set of two programs, both of which are able to print either of the two, depending on the command line argument supplied. Theoretically, there is no limit on the number of languages in a multiquine. A 5-part multiquine (or pentaquine) has been produced with Python, Perl, C, NewLISP, and F# and there is also a 25-language multiquine. Polyglot Similar to, but unlike a multiquine, a polyglot program is a computer program or script written in a valid form of multiple programming languages or file formats by combining their syntax. A polyglot program is not required to have a self-reproducing quality, although a polyglot program can also be a quine in one or more of its possible ways to execute. Unlike quines and multiquines, polyglot programs are not guaranteed to exist between arbitrary sets of languages as a result of Kleene's recursion theorem, because they rely on the interplay between the syntaxes, and not a provable property that one can always be embedded within another. Radiation-hardened A radiation-hardened quine is a quine that can have any single character removed and still produces the original program with no missing character. Of necessity, such quines are much more convoluted than ordinary quines, as is seen by the following example in Ruby: eval='eval$q=%q(puts %q(10210/#{1 1 if 1==21}}/.i