cartel is a formal (explicit) “agreement” among competing firms. It is a formal organization of producers and manufacturers that agree to fix prices, marketing, and production.[1] (…) The aim of suchcollusion (also called the cartel agreement) is to increase individual members’ profits by reducing competition.
(…)
Competition laws often forbid private cartels. Identifying and breaking up cartels is an important part of the competition policy in most countries, although proving the existence of a cartel is rarely easy, as firms are usually not so careless as to put collusion agreements on paper.[2][3]

Let’s look at the data:

 All of the above competing companies offer 4 months at 50% discount and exact same prices (within a margin of Eur 0,01)

See also (Portuguese legislation forbidding collusion):

CAPÍTULO II

Práticas restritivas da concorrência

SECÇÃO I

Tipos de práticas restritivas

Artigo 9.º

Acordos, práticas concertadas e decisões
de associações de empresas

1 – São proibidos os acordos entre empresas, as práticas concertadas entre empresas e as decisões de associações de empresas que tenham por objeto ou como efeito impedir, falsear ou restringir de forma sensível a concorrência no todo ou em parte do mercado nacional, nomeadamente os que consistam em:
a) Fixar, de forma direta ou indireta, os preços de compra ou de venda ou quaisquer outras condições de transação;

Disclaimer:

All contents on this post were collected on the 5th July 2013. 
There is absolutely no original thought here, only:
– a clear exhibition of the publicly available information from the companies 
– a definition exert from Wikipedia.
– a quotation of the legislation