books.google.co.uk - Perhaps the most important work of philosophy written in the twentieth century, Tractatus Logico-Philosophicus was the only philosophical work that Ludwig Wittgenstein published during his lifetime. Written in short, carefully numbered paragraphs of extreme brilliance, it captured the imagination of...http://books.google.co.uk/books/about/Tractatus_Logico_Philosophicus.html?id=IgxtIPcXQpAC&q=formal+concept&utm_source=gb-gplus-shareTractatus Logico-Philosophicus
