(1)Vin is the smartest guy that can play a piano.
(2)Vin is the smartest guy in the class that can play a piano.
(3)Vin is the smartest guy in the class that can understand every kind of algebra and calculus.
I asked my grammar teacher about the meaning of the first one today, and she said that means "there are many people who can play a piano, and Vin is one of them, and he is the smartest."
I thought that made sense, so I came up with another example(which is the number two) and asked. She just replied "there is no such kind of usage." I just said to myself "what!? there are plenty of them!"
So, please help me with (2) and (3)! And, I'd like to try to explain (2) and (3) because I think that may make it easier for you guys to help me^^
My explanation to (2) is: Vin is the smartest in the class, and he can play a piano.(I don't think it implies "there are classmates who play a piano, and Vin is the smartest one in them." I think the meaning of (2) is different from (1). Maybe it is ambiguous so it could be explained that way?)
My explanation to (3) is: Vin is the smartest guy in the class, and he can understand every kind of algebra and calculus.(kind of like the (2))
About (3), there is a similar sentence on the net:
Sailor Algebra: The smartest guy in the universe that can understand every kind of algebra and calculus.
from http://uncyclopedia.wikia.com/wiki/Sailor_Moon/List_of_minor_Sailor_Moon_characters