Hopefully this translates well into English..

A man is sitting on a park bench reading a book called "Logic" and another man walking past sits down beside him and asks what logic means..
The man reading the book asks, "Well, do you have an aquarium at home?"
"Yes! I do!"
"So I'm guessing you have fish in your aquarium?"
"I do!"
"And if you have fish in your aquarium, I'm guessing you like animals..?"
"Yes, I like animals!"
"And if you like animals, I would say you like people as well?"
"Yes, I like I people.."
"And if you like people, I guess you like women too?"
"Oh yes, I LOVE women!"
"Well there you go, that's what logic is!"
The man contemplates the answer he received and is satisfied with it and is about to get up to leave, when he asks: "What would've happened if I said that I didn't have an aquarium at home?"
The man on the bench thinks to himself for a minute and answers, "Well, you would've obviously been gay then".