[Python] Subset rows in df where first two string values are the same - python

I'm aiming to subset a df where the first two string values in a list are the same between two separate columns. Example, the list outlined in first_2 display the values I'm interested in returning. When these values are found between Letters and Value, I want to subset these rows.

However, I don't want the rows where AB and DA are found. I'm only after an identical match.

df = pd.DataFrame({
'Letters''AB','BD','AB','DA','EG','FA'),
'Value''AB','BC','DA','DA','EH','FA'),
'Position'1,np.nan,3,4,np.nan,6),
})

first_2 = ['AB','DA']

df1 = df[(~df['Letters'].str[0:1].isin(first_2)) & (df['Value'].isin(first_2))]


intended:

Letters Value Position
0 AB AB 1.0
3 DA DA 4.0

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