diff --git a/notsof.md b/notsof.md
index 028b74885..3f772efd0 100644
--- a/notsof.md
+++ b/notsof.md
@@ -2,6 +2,7 @@
 
 - [[pull]] [[notes-on-the-synthesis-of-form]]
 - [[go]] https://via.hypothes.is/stoa.anagora.org/notsof.pdf
+- [[systems]], [[models]]
 
 ## [[2021-03-17]]
 
@@ -13,6 +14,7 @@
 - Ensembles can be decomposed into many (nested, overlapped) [[form-context boundaries]].
   - But in any given analysis the boundary should probably be kept constant.
 - [[p19]] "The form is a part of the world over which we have control, and which we decide to shape while leaving the rest of the world as it is. The context is that part of the world which puts [[demands]] on this form; anything in the world that makes demands of the form is context. [[Fitness]] is a [[relation]] of [[mutual acceptability]] between these two. In a problem of design we want to satisfy the mutual demands which the two make on one another. We want to put the context and the form into [[effortless contact]] or [[frictionless coexistence]]."
+- [[p20]] interesting/surprising use of [[impossible]].
 
 [//begin]: # "Autogenerated link references for markdown compatibility"
 [pull]: pull "Pull"