Hierarchical Document Summarizer

Build a hierarchical summarization system for long documents.

## Document Types
{{document_types}}

## Summary Requirements
{{summary_requirements}}

## Token Constraints
{{token_constraints}}

Implement hierarchical summarization:

```python
class HierarchicalSummarizer:
    def segment_document(self, document: str) -> List[Section]:
        """Divide into logical sections"""
        pass
    
    def summarize_section(self, section: str, target_ratio: float) -> str:
        """Create section summary"""
        pass
    
    def build_summary_tree(self, sections: List[str], depths: int) -> SummaryTree:
        """
        Create hierarchical summary:
        - Level 1: Section summaries
        - Level 2: Group summaries
        - Level 3: Document summary
        """
        pass
    
    def generate_at_level(self, tree: SummaryTree, level: int) -> str:
        """Get summary at specified detail level"""
        pass
```

Include:
- Coherence preservation
- Key information retention
- Cross-reference handling
- Adaptive depth selection