Dear Students, My lifelong scientific pursuits and some personal researches, which, alas, did not gain international recognition, persuade me to believe in the existence of a new, versatile and elusive substance: leaverite. It is hard to find a precise definition, or even an exhaustive list of physical characteristics. What is certainly known about it is that it can be found in scientists' labs and offices. You know, you look around, among test tubes, books and various other knicknacks and you suddenly spot it. You take it in your hand, turn is around, and then ask puzzled: "What is this?" And promptly comes the answer: "Leaverite there." The natural feeling, when encountering leaverite, is to take it with you, to collect it for further examination. And so this little pest accumulates in huge amounts, creating an artificial habitat, turning your entire life into its personal ecosystem. Recent and disturbing data warn that leaverite has begun expanding its habitat, leaving the labs, universities and scientific institutions and making its insidious way into our own homes, simple, private persons with no connection to Geology or other branches of natural sciences. Here are a few reports. "Hi, Dad! Cool gadget! What is it?" "Leaverite there, son." (Click, click and the cozy atmosphere of the room turns Arctic cold.) "Boss, some guys in uniform came earlier and left this. What is it?" "Leaverite there, Molly." (Punch, click and a deafening sounds sends the surveillance team into maximum alert.) And here's my personal favorite: "Cool key! What's it for, dad?" "Leaverite there, boy!" (The youngster judiciously puts the key in his pocket, nicks another beer and takes the car for a ride, crashing it in the first tree.) As you can see, leaverite is a very dangerous, devious substance. It can appear from nowhere and wreak havoc into our lives. So whenever you see it and feel the urge to make further inquiries into its nature, be strong! Resist its almost supernatural power. Never, ever take it into your hand and ask what it is. This simple precaution may save your life. Thank you for your attention! Now, then, what is this little shiny thing on the floor? (A chorus of students) "LEAVERITE THERE!"