Degrees of Prohibition

Ok, we've been forewarned. Here's a list of people we can't marry! (Courtesy of the Registry of Marriages in Singapore ) Mind you, it's pretty much an idiot's guide with the terminology.

Question is, was it necessary to state that i can't marry my daughter's (if i have one) husband, bearing in mind that i already can't marry him because he is already legally married? Hmm..