4-1 Boolean Operations and Expressions Boolean algebra(布尔代数) is the mathematics of digital systems ◆ Sum term(和的形式): is a sum of literals(文字) a variable or the complement of a variable), produced by an or gate X=A+B.X=A+B.X=a+btc+D a sum term is equal to I when one or more of the literals in the term are 1 a sum term is equal to o only if each of the literals is 010 4-1 Boolean Operations and Expressions  Boolean algebra (布尔代数） is the mathematics of digital systems.  Sum term （和的形式）: is a sum of literals (文字) ( a variable or the complement of a variable), produced by an OR gate.  A sum term is equal to 1 when one or more of the literals in the term are 1.  A sum term is equal to 0 only if each of the literals is 0. X = A+ B, X = A+ B, X = A + B +C + D