I dislike books that have poor indexes and absent glossaries, but the book I'm chomping through on teaching elementary math has a convoluted sentence with the gist that "the closure prinicple of addition and multiplication for whole numbers is extended to include the closure principle of division when applied to fractional computation". I googled several combos of "closure principle" + other words, and got mostly philosophical websites, a few religious web sites and even some mathematical web sites that didn't define or give an example of the "closure principle", but assumed you knew the meaning already. It isn't in my chemistry or biology dictionary (big surprize). Help. TIA blacksalt OT: Thrill of the day: I met a woman named Xanthippe today! I also met someone trying to commit suicide via voodoo...i.e. hanging an effigy of herself. They were not one and same people.