A quantum effect is an operator
A on a complex Hilbert space
H that satisfies
0≤A≤I,
E(H) is the set of all quantum effects on
H. In 2001, Professor Gudder and Nagy studied the sequential product
A∘B=A1/2BA1/2 of
A,B∈E(H). In 2005, Professor Gudder asked: Is
A∘B=A1/2BA1/2 the only sequential product on
E(H)? Recently, Liu and Wu presented an example to show that the answer is negative. In this paper, firstly, we characterize some algebraic properties of the abstract sequential product on
E(H); secondly, we present a general method for constructing sequential products on
E(H); finally, we study some properties of the sequential products constructed by the method