i am trying to write code to do a local validation.

assume ground truth is:

```
['abc' 'de' 'fgh'] , len=18
```

if my prediction is:

```
['abc' 'd' 'fg'], len=16
```

is the score = 1- Levenshtein(predict,truth)/len(truth) = 1-2/18 ?

or are we using

1- Levenshtein(predict,truth)/len(predict) , etc …

will the score be negative if Levenshtein(predict,truth) > len