diff --git a/python/frep.py b/python/frep.py
index 34f9944ab89d6d229d2953666009658ef915a5e4..e785afa6569b1f812d21573cf5078105a7b36ed5 100755
--- a/python/frep.py
+++ b/python/frep.py
@@ -3,8 +3,11 @@
 # frep.py
 #    functional representation solver
 #
-# usage
+# usage:
 #    pcb.py | frep.py [dpi [filename]]
+# with:
+#    https://gitlab.cba.mit.edu/pub/libraries/blob/master/python/pcb.py
+#
 #
 # Neil Gershenfeld 10/8/18
 # (c) Massachusetts Institute of Technology 2018
diff --git a/python/pcb.py b/python/pcb.py
index b0e969d17913b54db42958ebaa917d6bc887c810..fc1b8ccb425550bf80480e9c41aa324e0b70a1c6 100755
--- a/python/pcb.py
+++ b/python/pcb.py
@@ -2,6 +2,11 @@
 #
 # pcb.py
 #    functional representation PCB template
+
+# usage:
+#    pcb.py | frep.py [dpi [filename]]
+# with:
+#    https://gitlab.cba.mit.edu/pub/libraries/blob/master/python/frep.py
 #
 # Neil Gershenfeld 10/8/18
 # (c) Massachusetts Institute of Technology 2018