How to check the same value in two tables on the same page in Google Tables?

Question

Google Sheets

There is a formula by which you can find out if a value is repeated in cells:

=AND(NOT(ISBLANK(A1)); COUNTIF($A3:$A; "=" & A1) > 1)

It will show where the duplicate values ​​are.
I can't write strictly for two tables so that the check is only between them.
The range is A1:C , the tables are located: 1st in A, 2nd in C.
I tried with an array:

=AND(NOT(ISBLANK(A1)); COUNTIF({$A3:$A; $C3;$C}; "=" & A1) > 1)

Tried COUNTIFS:

=AND(NOT(ISBLANK(A1)); COUNTIFS($A3:$A; "=" & A1; $C3;$C; "=" & A1;) > 1)

Does not exceed. Please tell me how to make it work.

Answer 1

You have not yet answered the clarifying question in the comment, so you will have to guess what exactly is needed.
1) Suppose that you need to select those cells that are in both columns (A and C).
Select the first one, add Conditional Formatting - Your formula . Enter: Select the second column (let's say C), and do the same, but this time the formula is: 2) Let's assume that we just need to select duplicates in two non-adjacent ranges. Select both by holding Ctrl and paste into the UV formula:
In both cases, the data is assumed to be in columns A and C, starting directly from the first cell. Don't forget to change the links to yours