How to remove duplicate row in file

Linux
,

Suppose there are two files,

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A
aaa
bbb
ccc
ddd

B
aaa
bbb
eee
fff

How to remove duplicate rows?

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aaa
bbb
ccc
ddd
eee
fff
1
cat A B | sort | uniq

How to get intersection?

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aaa
bbb
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cat A B | sort | uniq -c | awk -F " " '{if($1!=1) print $2;}'