A system includes several pairable elements and elements to be used for such a system. Each of the elements is adapted to be combined with another element, thereby constituting a pair of elements. The elements include a first indicator where when combining the first indicator of a first element and the first indicator of a second element in a manner specific to the first indicators, the combined first indicators indicate if the first and second elements are a pair. Further, elements include a second indicator where when combining the second indicator of the first element and a second indicator of the second element in an manner specific to the second indicators, the combined second indicators indicate if the elements are a pair and if they are not a pair, the combined second indicators identify the right element to pair with said first and second element.