19. U.S. TreasuryDirect. “Call Protection: Noncallable Marketable Securities.” TreasuryDirect Glossary. Accessed August 26, 2025. Clarifies that modern Treasury notes and bonds cannot be called by holders or issuer.
20. Financial Stability Board and BIS. “Lessons from March 2020: Market Dysfunction and the Role of Central Banks.” Joint Reports, 2020–2021. Analyzes safe-asset fragility and the stabilizing function of an independent central bank.