※ 引述《OKOK98 (忙忙忙)》之銘言：
: 離散數學
: Let A(x) denote the ordinary generating function of the sequence of numbers
: (a0,a1,a2,a3...). Find the sequence whose ordinary generating function is
: A(x)(1-x).(1-x is therefore called the difference operator.)
(a0 + a1x + a2x^2 ... )(1-x)
= a0 + (a1-a0)x + (a2-a1)x^2 + ...
so , a0 , a1-a0 , a2-a1 ...
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