In this part, you will write code
to compute LM probabilities for a trigram model smoothed
with “`+delta`” smoothing. This is just like “add-one” smoothing
in the readings,
except instead of adding one count to each trigram, we will add
`delta` counts to each trigram for
some small `delta` (*e.g.*, `delta=0.0001` in
this lab). This is just about the simplest smoothing algorithm
around, and this can actually work acceptably in some situations
(though not in large-vocabulary ASR). To estimate the
probability of a trigram
`P _{+delta}(w_{i} | w_{i-2} w_{i-1})`
with this smoothing, we take

Your job in this part is to fill in the function
`get_prob_plus_delta()`

. This function should
return the value
`P _{+delta}(w_{i} | w_{i-2} w_{i-1})`
given a trigram

Your code will again be compiled into the program **EvalLMLab3**.
To compile this program with your code, type

smk EvalLMLab3 |

lab3p2a.sh |

The instructions in `lab3.txt` will ask you to run the
script `lab3p2b.sh`, which does the same thing as
`lab3p2a.sh` except on a different test set.