Isaac Samuel Reggio (YaShaR) (1784-1855) was the author of A Guide for the Religious Instruction of Jewish Youth. He was an Austro-Italian scholar and rabbi born at Göritz, Illyria. Reggio studied Hebrew and rabbinics under his father, Abraham Vita, later rabbi of Göritz, acquiring at the same time in the gymnasium a knowledge of secular science and languages. Reggio's father, one of the liberal rabbis who supported Hartwig Wessely, paid special attention to the religious instruction of his son, who displayed unusual aptitude in Hebrew, and at the age of fourteen wrote a metrical dirge on the death of Moses Hefez, rabbi of Göritz. Besides Italian, his mother tongue, Reggio knew French, German, and Latin, and he studied several Semitic languages in addition to Hebrew. He possessed a phenomenally clear, if not profound, intellect, and as mathematics offered the widest field for his analytical talent, it was at first his favorite study. In 1802 he published in the Neuwieder Zeitung the solution of a difficult mathematical problem, which gave him reputation as a mathematician. He discovered also a new demonstration of the Pythagorean Theorem.