You can use diary sexps (
https://www.gnu.org/software/emacs/manual/html_node/emacs/Sexp-Diary-Entries.html).
For example:

* TODO something Mon, Wed and Fri
  SCHEDULED: <%%(memq (calendar-day-of-week date) '(1 3 5))>

See the bottom of https://orgmode.org/manual/Deadlines-and-scheduling.html

I don't use this, so I don't know what the practical limitations are.

John

-----------------------------------
Professor John Kitchin
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
@johnkitchin
http://kitchingroup.cheme.cmu.edu


On Thu, Apr 5, 2018 at 12:11 AM, Cecil Westerhof <cldwesterhof@gmail.com>
wrote:

> I have an event that I like to repeat three times a week: on Monday,
> Wednesday en Friday. Do I need three entries like:
> * TODO Do It
>   SCHEDULED: <2018-04-06 Fri ++1w>
> * TODO Do It
>   SCHEDULED: <2018-04-09 Mon ++1w>
> * TODO Do It
>   SCHEDULED: <2018-04-11 Wed ++1w>
>
> Or is there a better way?
>
> --
> Cecil Westerhof
>