diff --git a/RELEASE b/RELEASE
index cb4b1749d..2a004f7ab 100644
--- a/RELEASE
+++ b/RELEASE
@@ -1,5 +1,6 @@
                                   EYE release
 
+v4.17.2 (2023-09-23) reverting unify/2 wrt double negation
 v4.17.1 (2023-09-21) reverting to graffiti as list terms
 v4.17.0 (2023-09-20) graffiti as a set of blank nodes i.e. ($ bnodes $)
 v4.16.6 (2023-09-19) reverting graffiti to be list terms
diff --git a/VERSION b/VERSION
index 1b0a87fdf..1c8fd19fc 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-4.17.1
+4.17.2
diff --git a/eye.pl b/eye.pl
index 0bcd27114..4ac5f47c5 100644
--- a/eye.pl
+++ b/eye.pl
@@ -21,7 +21,7 @@
 :- use_module(library(pcre)).
 :- catch(use_module(library(http/http_open)), _, true).
 
-version_info('EYE v4.17.1 (2023-09-21)').
+version_info('EYE v4.17.2 (2023-09-23)').
 
 license_info('MIT License
 
@@ -10936,22 +10936,6 @@
     !,
     getlist(A, C),
     C = B.
-unify(A, B) :-
-    nonvar(A),
-    A = '<http://www.w3.org/2000/10/swap/log#onNegativeSurface>'([], '<http://www.w3.org/2000/10/swap/log#onNegativeSurface>'([], C)),
-    C \= false,
-    conj_list(C, D),
-    \+member('<http://www.w3.org/2000/10/swap/log#onNegativeSurface>'(_, _), D),
-    !,
-    unify(C, B).
-unify(A, B) :-
-    nonvar(B),
-    B = '<http://www.w3.org/2000/10/swap/log#onNegativeSurface>'([], '<http://www.w3.org/2000/10/swap/log#onNegativeSurface>'([], C)),
-    C \= false,
-    conj_list(C, D),
-    \+member('<http://www.w3.org/2000/10/swap/log#onNegativeSurface>'(_, _), D),
-    !,
-    unify(C, A).
 unify(A, B) :-
     nonvar(A),
     nonvar(B),
diff --git a/eye.zip b/eye.zip
index cc2a91512..a0a3b0fc2 100644
Binary files a/eye.zip and b/eye.zip differ
diff --git a/reasoning/blogic/modal.n3s b/reasoning/blogic/modal.n3s
index a11f50936..a211ffa89 100644
--- a/reasoning/blogic/modal.n3s
+++ b/reasoning/blogic/modal.n3s
@@ -15,7 +15,7 @@
     } .
 } .
 
-# it is obliged for bob to keep dogs
+# it is obliged for bob to keep dogs and sheep
 () log:onNegativeSurface {
     () log:onModalSurface {
         :Bob :keeps :Dogs, :Sheep.
@@ -34,14 +34,14 @@
             } .
         } .
     } .
-    # is it not permitted for bob to not keep dogs?
+    # is it not permitted for bob to not keep dogs and sheep?
     () log:onNegativeSurface {
         () log:onModalSurface {
-            () log:onNegativeSurface {
-                () log:onNegativeSurface {
+            #() log:onNegativeSurface {
+            #    () log:onNegativeSurface {
                     :Bob :keeps :Dogs, :Sheep .
-                } .
-            } .
+            #    } .
+            #} .
         } .
     } .
     # answer
diff --git a/reasoning/blogic/neutral.n3s b/reasoning/blogic/neutral.n3s
index 6cba89285..16ec93efc 100644
--- a/reasoning/blogic/neutral.n3s
+++ b/reasoning/blogic/neutral.n3s
@@ -58,12 +58,12 @@
     # check that necessity(A) = ~possibility(~A)
     () log:onNegativeSurface {
         () log:onNeutralSurface {
-            () log:onNegativeSurface {
-                () log:onNegativeSurface {
+            #() log:onNegativeSurface {
+            #    () log:onNegativeSurface {
                     :m :n :o .
                     :p :q :r .
-                } .
-            } .
+            #    } .
+            #} .
         } .
     } .
     () log:onAnswerSurface {
diff --git a/reasoning/blogic/version.n3s.out b/reasoning/blogic/version.n3s.out
index da711dcb7..a330eac62 100644
--- a/reasoning/blogic/version.n3s.out
+++ b/reasoning/blogic/version.n3s.out
@@ -1,3 +1,3 @@
 @prefix log: <http://www.w3.org/2000/10/swap/log#>.
 
-() log:version "EYE v4.17.1 (2023-09-21)".
+() log:version "EYE v4.17.2 (2023-09-23)".