Mac Duffee, C. C. Covariants of differential forms of arbitrary order and degree. (English) JFM 50.0454.07 American M. S. Bull. 30, 223 (1924). JFM Section:Weitere Literatur. PDFBibTeX XMLCite \textit{C. C. Mac Duffee}, Bull. Am. Math. Soc. 30, 223 (1924; JFM 50.0454.07)