Translated for Atractor by Gabriela Chaves, from its original version in Portuguese. Atractor is grateful for her cooperation.

(*) Since many browsers are blocking Java nowadays, it was decided to convert to Javascript the original applets of this section. This conversion was carried out within the scope of a support received from FCT - Fundação para a Ciência e a Tecnologia, through FACC (Fundo de Apoio à Comunidade Científica).

Difficulty level: University