For example example, min support=2 and the last freqent itemest in L4 is {1,2,3,4};
so we generate association rules for {1,2,3,4} - the last frequent itemset.
do we also need to  generate association rules for all frequent itemests in L3 ,L2,L1?
Example:
C1   L1        C2   L2         C3     L3             C4         L4                    C5     L5
                                                                        {1,2,3,4} =2         {}      {}

for example, In L1 ={1}, {2},{3},  so generate association rules as below?

1 -> 2
1 -> 3
2 -> 1
3 -> 1
2 -> 3
3 -> 2

In L2= {1,2}, {1,3}, the association rules  generated are

1 -> 2
2 -> 1
1 -> 3
3 -> 1

For those duplicated association rules ( eg. "1 -> 2" in both L1 and L2's outputs) , only output one instead of repeated "1 -> 2" ?

I got it. Thank you.