HollyFrontier Corporation filed SEC Form 8-K: Completion of Acquisition or Disposition of Assets, Entry into a Material Definitive Agreement, Material Modification to Rights of Security Holders, Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing, Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year, Other Events, Leadership Update, Regulation FD Disclosure, Financial Statements and Exhibits