Translation:Péter walks to those trees, where the red car stands.
OK, so is it acceptable to say "A fákhoz sétál Péter, ahol a piros autó áll" and if so does this mean "Peter walks to THE trees, where the red car stands"? I am not convinced there is really a difference in English between using a demonstrative pronoun and definite article here, as the second clause "where the red car stands" is in effect conditioning the definite article to be demonstrative.
There's a slight difference in meaning, which is not too important in this particular sentence, but it's clearer in other cases (though, of course, if English doesn't make a difference between the sentences of these pairs, both should be acceptable):
- "Segített nekem Péter, aki itt lakik." -- Péter helped me. By the way, he lives here.
"Segített nekem az a Péter, aki itt lakik." -- Out of the many Péters that one helped me who lives here.
"A városban voltam, ahol sok kastély van." -- I was in the city. By the way, there are many castles there.
- "Abban a városban voltam, ahol sok kastély van." -- Out of all the cities of this region I was in the one where there are many castles.