(defconst org-file-apps-defaults-cygwin
'((remote . emacs)
(t . "cygstart %s")
(system . "cygstart %s")
("ps.gz" . "gv %s")
("eps.gz" . "gv %s")
("dvi" . "xdvi %s")
("fig" . "xfig %s")))
(defun org-default-apps ()
"Return the default applications for this operating system."
(cond
((eq system-type 'darwin) org-file-apps-defaults-macosx)
((eq system-type 'cygwin) org-file-apps-defaults-cygwin)
((eq system-type 'windows-nt) org-file-apps-defaults-windowsnt)
(t org-file-apps-defaults-gnu)))
And it works for me so far. Your code is more compact but an ad-hoc solution as well. It is worth to take into consideration. Thanks again.
I suppose you would like to know I have also tweaked your directions about odt-mathml for cygwin:
(setq org-latex-to-mathml-convert-command
"java -jar $(cygpath -pw %j) -unicode -force -df %o %I")
(setq org-latex-to-mathml-jar-file
"/home/user/tmp-odt/mathtoweb.jar")
with great success (Java 1.7 update 25, mathtoweb 4.0.0).
Miguel.