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1 files changed, 6 insertions, 2 deletions

diff --git a/doc/undo.md b/doc/undo.md
index 4afa2c00..fe27fa37 100644
--- a/doc/undo.md
+++ b/doc/undo.md
@@ -18,7 +18,7 @@ Here it undoes a function to decrement the last character by incrementing that c
 
 ## The rules
 
-If `�` can be inverted exactly, then Undo just does that. However, there are also some other functions that BQN inverts. For example, the squaring function `ט` has both a positive and a negative inverse, and yet:
+If `�` can be inverted exactly, then Undo just does that (or tries). However, there are also some other functions that BQN inverts. For example, the squaring function `ט` has both a positive and a negative inverse, and yet:
 
         ט ¯3
         ט� ט ¯3  # It's not the same!
@@ -40,6 +40,7 @@ A few notable inverses are the [logarithm](arithmetic.md#basic-arithmetic) `⋆â
 Structural functions like [Take](take.md) and [shifts](shift.md) that remove elements from `�` can't be inverted, because given the result there's no way to know what the elements should be. However, there are two special cases that have inverses defined despite losing data: these are `⊣�` and `k�` where `k` is a constant (a data type, or `k˙`). For these, `�` is required to [match](match.md) the always returned value `�` or `k`, and this value is also used for the result—even though any result would be valid, as these functions ignore `�`.
 
         3 ⊣� 4
+
         3 ⊣� 3
 
 ## Undo headers
@@ -51,4 +52,7 @@ Of course BQN will never be able to invert all the functions you could write (if
       ���: �÷1-�
     }
 
-The above function could also be defined with the automatically invertible `1⊸+⌾÷`, but maybe there's a numerical reason to use the definition above. Like a normal header, an undo header reflects the normal use, but it includes `�` and possibly `˜` addition to the function and arguments.
+The above function could also be defined with the automatically invertible `1⊸+⌾÷`, but maybe there's a numerical reason to use the definition above. Like a normal header, an undo header reflects the normal use, but it includes `�` and possibly `˜` addition to the function and arguments. Any header that includes a function can have these modifiers added—even a fancy modifier header like `�_m1�a‿b:` or plain label like `��:`. The three forms are `���:`, `����:`, and `��˜��:`, and the two dyadic forms are also used to derive `k⊸F��` and `F⟜k��` with a constant `k`.
+
+        G � { �˜�:�-2×� ; �+2×� }
+        G⟜2� 7