Hi Wolfgang,

Thank you for your attention: in fact you pointed out how to solve the problem… 
Beginning with what you wrote, after a few trials and errors I ended up with the following which gives what I meant:
%%% begin reverse-enumeration.tex
\definenumber[ReverseNumberOrder][numberorder=reverse]

\defineenumeration[Lecture]
	[location=hanging,
	text={Lecture n° {\convertednumber[ReverseNumberOrder]}.}, 
	between=,
	before={\incrementnumber[ReverseNumberOrder]},
	number=no,
	after={\hrule\blank}]

\starttext

\startLecture Tuesday December 6th: Banach spaces. 
\startitemize[n]
\item First subject.
\item Second subject.
\stopitemize
\stopLecture

\startLecture Tuesday November 29th: Norms. 
\startitemize[n]
\item First subject.
\item Second subject.
\stopitemize
\stopLecture

\startLecture Tuesday November 22nd: Topological Vector Spaces. 
\startitemize[n]
\item First subject.
\item Second subject.
\stopitemize
\stopLecture

\stoptext
%%% end reverse-enumeration.tex

Best regards: OK

On 12 déc. 2011, at 14:03, Wolfgang Schuster wrote:

> 
> Am 12.12.2011 um 13:33 schrieb Otared Kavian:
> 
>> Hi all,
>> 
>> When using 
>> 	\startitemize[n,reverse]
>> one gets items numbered in reverse order. I wonder if this feature exists also for enumerations. An example is given below in which the last enumeration is written on top of the file and I wish it were possible to have the enumerations numbered in reverse order.
> 
> The numbering mechanism has indeed such a option but it seems to be not available for enumerations.
> 
> \definenumber[foo]
> \definenumber[bar][numberorder=reverse]
> 
> \define\test
>  {\incrementnumber[foo] \incrementnumber[bar]%
>   \convertednumber[foo]:\convertednumber[bar]}
> 
> \starttext
> \dorecurse{9}{\test\par}
> \stoptext
> 
> Wolfgang
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Otared Kavian
Département de Mathématiques
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