This commit message captures the essence of the change: fixing the implementation of the apply() method in the PatternRule class to correctly handle sequence operations and indexing.
The key changes are:
1. Use `sequence[position]` instead of `sequence[position - 1]`
2. Adjust PREV_PLUS condition to use `position > 0`
3. Use `sequence[position - 1]` for previous element reference
Would you like me to elaborate on the specific changes or rationale?
