# Relationship history for MSHA mine 0900881

Current hierarchy: **Asea Brown Boveri Ltd (ABB) → Yara Engineering Corp → Deepstep Division**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-13T11:19:05.459773+00:00

## Valid-time edges

- **operator_operates_mine:** Yara Engineering Corp → Deepstep Division; 1978-03-09 to 1980-09-30; source msha-controller-operator-history
- **controller_controls_mine:** Yara Engineering Corp → Deepstep Division; 1978-03-09 to 1980-09-30; source msha-controller-operator-history
- **controller_controls_operator:** Yara Engineering Corp → Yara Engineering Corp; 1978-03-09 to 1980-09-30; source msha-controller-operator-history
- **operator_operates_mine:** Yara Engineering Corp → Deepstep Division; 1980-10-01 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Asea Brown Boveri Ltd (ABB) → Deepstep Division; 1980-10-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Asea Brown Boveri Ltd (ABB) → Yara Engineering Corp; 1980-10-01 to current/open; source msha-controller-operator-history