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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 Form 6 - K REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a - 16 OR 15d - 16 OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30 , 2021 Commission File Number 001-39237 ATLAS CORP . ( Exact name of Registrant as specified in its Charter ) 23 Berkeley Square London , United Kingdom W1J 6HE ( Address of principal executive office ) Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20 - F or Form 40 - F . Form 20 - F Indicate by check mark if the registrant is submitting the Form 6 - K in paper as permitted by Regulation S - T Rule 101 ( b ) ( 1 ) . Yes Indicate by check mark if the registrant is submitting the Form 6 - K in paper as permitted by Regulation S - T Rule 101 ( b ) ( 7 ) . Yes Form 40 - FO No 冈 No 冈