DIED. Paul Gann, 77, crusading co-author (with Howard Jarvis) of California's tax-cutting Proposition 13; of pneumonia complicated by AIDS; in Sacramento. The Jarvis-Gann Initiative, overwhelmingly approved by California voters in 1978, cut the state's property taxes in half and inspired similar tax-revolt measures across the country. Gann developed AIDS two years ago from a blood transfusion received during heart surgery. While bearing no grudge against the donor, Gann believed that people who knowingly transmit the disease "should be tried for murder."