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, pronounced "parens", is a daughter of iota midwived by User:Dankogai which source code consists entirely of '(' and ')'.

JavaScript
var S = function(x){return function(y){return function(z){return x(z)(y(z))}}}; var K = function(x){return function(y){return x}}; var U = function(x){return x(S)(K)}; var iota2jsstr = function(str){ return (function(a){       if (!a.length) throw 'syntax error';        return a.shift === 'i'             ? 'U'             : arguments.callee(a) + '(' + arguments.callee(a) + ')';    })(str.replace(/[^\*i]/g, ).split()); }; var iota = function(str){ return eval(iota2jsstr(str)) }; var iota2parens = function(str){ return iota2jsstr(str).replace(/[^\(\)]/g, ''); }; var parens2jsstr = function(str){ return str.replace(/\(/g, 'U(') .replace(/U\(\)/g, 'U(U)') .replace(/\)U\(/g, ')('); }; var parens = function(str){ return eval(parens2jsstr(str)) };

Scheme
(define S (lambda (x) (lambda (y) (lambda (z) ((x z) (y z)))))) (define K (lambda (x) (lambda (y) x))) (define U (lambda (x) ((x S) K))) (define (%parens base compose)   (lambda (code) (let r ((c code))       (unless (list? c) (error "proper list required, but got" c))        (fold (lambda (a b) (compose b (r a))) base c)))) (define parens       (%parens U (cut <> <>))) (define parens->lisp (%parens 'U list)) (define parens->jsstr (%parens "U" (cut string-append <> "(" <> ")")))

Computational class
Turing complete, just as mother (also a twin sister!) iota is.

Notable Characteristics

 * a valid code is always one symbol shorter than its corresponding iota code.
 * the I combinator happens to be ''.

External resources

 * http://blog.livedoor.jp/dankogai/archives/51524639.html
 * http://d.hatena.ne.jp/youz/20101004/1286211969