Hi Wolfgang,

Thanks for having solved the problem with subformulas numbering.
I would just make a comment on your answers to Lukás, regarding the use of 
\startsubformulas[mylabel]

Indeed using this structure instead of 
\startsubformulas[+]
allows one to refer to all the sub-formulas by invoking (\in[mylabel]), but if one wishes to refer to any individual sub-formula one has to give a label inside the structure \start—\stop—subformulas, at the level of \placeformula for that sub-formula.
Below  is your example, with these remarks.

Thanks for your attention and help: OK
%%%% begin example
\usemodule[visual]

\starttext
Using the definition of the scalar product we infer that:
\placeformula[eq:1]
\startformula
\fakeformula
\stopformula
And here are some other relations valid in a Hilbert space:
%\startsubformulas[+]       % These two options for \subformulas
%\startsubformulas[mylabel] % enable subnumbers for the formulas

\startsubformulas
    \placeformula[eq:2-a]
    \startformula
    \fakeformula
    \stopformula

    \placeformula[eq:2-b]
    \startformula
    \fakeformula
    \stopformula

\stopsubformulas
It is clear that the equality (\in[eq:2-b]) is a consequence of (\in[eq:1]) and (\in[eq:2-a]).

% To test how to change the number separator
\defineseparatorset[none][][]
\setupformulas[numberseparatorset=none]

\startsubformulas[eq:3]
    \placeformula
    \startformula
    \fakeformula
    \stopformula

    \placeformula
    \startformula
    \fakeformula
    \stopformula

\stopsubformulas
Prove relations (\in[eq:3]) using (\in[eq:1]).
\stoptext
%%%% end example


On 06 Aug 2015, at 12:07, Wolfgang Schuster <schuster.wolfgang@gmail.com> wrote:

Hello Wolfgang,

thank you for the patch (not in today's beta); I also attach the modified strc-mat.mkiv and a test file.

Two questions:

1.

What exactly are

  %\startsubformulas[+]       % These two options for \subformulas
  %\startsubformulas[mylabel] % enable subnumbers for the formulas

intended for?

The simple "\startsubformulas[eq:b]" meets my needs (subformulas are sub-numbered) and I can't see any difference to "\startsubformulas[+]".
When you write \startsubformulas[-] the numbers for the formulas aren’t displayed in the output but the counter is still increased. I guess \startsubformulas[+] is just there for completeness sake because there are other functions with “-” and “+” options as well.

One difference between \startsubformulas[+] and \startsubformulas[label] is that the second method creates a label which can be used to refer to the number of the formula.
2.

Is there a way to setup numbering subformulas to "(1a)" form instead of "(1.a)", i.e. set the separator to ""?
You have to change the separator list with the numberseparator key for \setupformulas.

\defineseparatorset[none][][]
\setupformulas[numberseparatorset=none]

Wolfgang
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