An Israeli institute that specializes in inventing devices religious Jews can use on the Sabbath without violating the biblical writ forbidding work has come up with a $10 pen that it claims fills the bill.

The pen, developed by the Tsomet Institute, is called a "Shabet" - a word play on Sabbath and "et," or pen in Hebrew.Rabbi Israel Rosen, institute director, said the pen was invented for religious doctors and policemen and is kosher because the ink it uses disappears after a few days, becoming literally "non-existent."

Jewish religious law forbids work on the Sabbath other than a lifesaving action. Among Tsomet's inventions is an electric timer - or Sabbath clock - that turns lights on and off since that action is considered work by the religious.

Rami Sadan, a spokesman for Israel's chief rabbis, said Chief Rabbi Mordechai Eliahu of the Sephardic community of Middle Eastern Jews helped develop the Shabet pen and has approved it.

Rabbi Shimon Stern, of the Scientific Institute for Halachic (religious law) Affairs, Tsomet's competitor, said his institute has tried to develop a special `Sabbath' paper on which writing would fade.

A disappearing-ink pen, he noted, could be used to fill out a check.