The only place I've been able to find the PDF of Ted Harding's "A Guide to Typesetting Mathematics using GNU eqn" (the link from troff.org is broken) is in the archives of the groff mailing list:
https://lists.gnu.org/archive/html/groff/2013-10/pdfTyBN2VWR1c.pdf Does anyone know of the source to this was ever released? -- T. Kurt Bond, tkurtb...@gmail.com, https://tkurtbond.github.io