diff --git a/lib/__init__.py b/lib/__init__.py
index c835149..4511c25 100644
--- a/lib/__init__.py
+++ b/lib/__init__.py
@@ -43,7 +43,7 @@ def neonpink(xs):
     return tilter2(xs, 'raw')
 
 def c_render(cascade, precision=4096):
-    # TODO: deprecate in favor of tilter2 (which also needs to be renamed)
+    # TODO: deprecate in favor of tilter2
     xs = xsp(precision)
     return xs, tilter2(xs, cascade)
 
@@ -102,7 +102,7 @@ def tilter(xs, ys, tilt):
     lament("tilter(): DEPRECATED; use ys -= tilter2(xs, tilt) instead.")
     return xs, ys - tilter2(xs, tilt)
 
-def tilter2(xs, tilt):
+def tilter2(xs, tilt): # TODO: rename
     noise = np.zeros(xs.shape)
     if isinstance(tilt, str) and tilt in cascades:
         tilt = cascades[tilt]
diff --git a/lib/planes.py b/lib/planes.py
index 1f51768..9a212bd 100644
--- a/lib/planes.py
+++ b/lib/planes.py
@@ -3,6 +3,11 @@ from . import tau
 import numpy as np
 import sympy as sym
 
+# implements the modified bilinear transform:
+# s <- 1/tan(w0/2)*(1 - z^-1)/(1 + z^-1)
+# this requires the s-plane coefficients to be frequency-normalized,
+# and the center frequency to be passed as a transformation parameter.
+
 def zcgen_py(n, d):
     zcs = np.zeros(d + 1)