add discussion to calc

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diff --git a/2025/talks/calc.md b/2025/talks/calc.md
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--- a/2025/talks/calc.md
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@@ -17,6 +17,41 @@ About the speaker:
 
 Christopher Howard is a simulator technician in Fairbanks, Alaska, and a GNU Emacs user for a little over a decade. My technical interests are focused on analog computing and modeling with differential equations.
 
+## Discussion / notes
+
+-   Q: How sophisticated an ordinary differential equation solver would
+    be useful? There are some C libraries one ould try to build upon,
+    but there are many corner cases, stiff, non-stiff is one
+    categorization, but an explicit Runge Kutta would work for many
+    non-stiff equations
+    -   A: I don't really have any opinions right now about the
+        approximation methods. For me, what I really want is one of
+        those old style languages where you basically just type in the
+        list of differential equations and don't have to do any other
+        computer programming, or know the details of another programming
+        language. I played around a bit with python-dda, though it has
+        some deficiencies. There are some graphical free software
+        programs where you do this sort of thing with blocks, but they
+        all depend on Java which is problematic in Guix.
+-   Q: Is there a way to see the input of a custom function? E.g. if you
+    forget the order of f and C in the example you showed
+    -   A: Let's see... there is calc-user-define-edit. One calc also
+        view the file where the definitions are stored, though that is a
+        somewhat obscure format.
+-   Q: Have you tried interacting with calc via org-babel (first thing
+    that came to mind when you said that you'd like to annotate
+    values)? Any thoughts on that? How about rendering gnuplots on org
+    documents via calc?
+    -   A: I played around with org-babel a few years ago but haven't
+        really had any need or interest in it of late.
+- Q: Who is in charge of calc development anyway? Is there an active maintainer?
+- Nice talk.
+- Thanks for the cool talk! I've been using Calc quite a lot recently for linear algebra work. I also use it quite often for unit conversion. There's a package called calc-currency which is very useful but unfortunately does not seem to be maintained anymore.
+- I'm going to have to rewatch this talk.
+- thanks for your talk! Calc strikes me as one of those really powerful things I should spend time learning a little more about one of these days =)
+- calc is suprisingly good at datetime math.
+- I mostly use it for that and unit conversion.  I don't do any fancy calculus like lispmacs did in his talk.
+- Funny, I'm studying computer engineering and just a few weeks ago I'd decided to properly learn how to use calc myself.
 
 
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