How to check if a particular value in a list is equal to a value in another list using if statement?

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Python3.6

if
a=[1,2,3,4,5]
b=[6,7,8,5,9]
how to check if a[4]=a[3]?
what code should i write if it should be true?

This is the code i have made.
----------------------------

dict={}
a=[1,2,3,4,3,1,2,8,9,10]
b=[]
b+=a
for i in a:
    for j in b:
        dict[a[i]]=j
print(min(dict,key=dict.get))

What I have tried:

I have used this to find the duplicate value with the minimum index.
but if statement dosent work. why is it?

dict={}
a=[1,2,3,4,3,1,2,8,9,10]
b=[]
b+=a
for i in a:
    for j in b:
        dict[a[i]]=j
print(min(dict,key=dict.get))