Jurafsky's book says we need to add context to left and right of a sentence:
Does this mean,
for example, if we've a corpus of three sentences: "John read Moby Dick", "Mary read a different book", and "She read a book by Cher"; and after training our tri-gram model on this corpus of three sentences, we need to evaluate the probability of a sentence "John read a book", i.e. to find $P(John\; read\; a\; book)$ as below,
$P(John\; read\; a\; book)$
$=P(<s><s>John\; read\; a\; book<\backslash s><\backslash s>)$
$=P(John|<s><s>) P(read|<s>John) \; P(a|John\; read) P(book|read\; a) P(<\backslash s>|a\; book)\; P(<\backslash s>|book<\backslash s>)$
$=\frac{1}{3}\frac{1}{1}\frac{1}{1}\frac{1}{2}\frac{0}{1}\frac{1}{1}$ (without smoothing)
It would be great, if you let me know if the above understanding is correct?
