3 files changed, 22 insertions, 4 deletions

diff --git a/src/alg.c b/src/alg.c
index 2b5b93f..6a16d9a 100644
--- a/src/alg.c
+++ b/src/alg.c
@@ -6,6 +6,7 @@ static bool        allowed_HTM(Move m);
 static bool        allowed_URF(Move m);
 static bool        allowed_eofb(Move m);
 static bool        allowed_drud(Move m);
+static bool        allowed_drud_noD(Move m);
 static bool        allowed_htr(Move m);
 static bool        allowed_next_HTM(Move l2, Move l1, Move m);
 static int         axis(Move m);
@@ -46,6 +47,12 @@ moveset_drud = {
 };
 
 Moveset
+moveset_drud_noD = {
+        .allowed      = allowed_drud_noD,
+        .allowed_next = allowed_next_HTM,
+};
+
+Moveset
 moveset_htr = {
         .allowed      = allowed_htr,
         .allowed_next = allowed_next_HTM,
@@ -57,6 +64,7 @@ static Moveset * all_ms[] = {
         &moveset_URF,
         &moveset_eofb,
         &moveset_drud,
+        &moveset_drud_noD,
         &moveset_htr,
 };
 
@@ -95,6 +103,15 @@ allowed_drud(Move m)
 }
 
 static bool
+allowed_drud_noD(Move m)
+{
+        Move b = base_move(m);
+
+        return b == U ||
+               ((b == R || b == L || b == F || b == B) && m == b + 1);
+}
+
+static bool
 allowed_htr(Move m)
 {
         Move b = base_move(m);
diff --git a/src/alg.h b/src/alg.h
index 8f55c15..7d11a7d 100644
--- a/src/alg.h
+++ b/src/alg.h
@@ -12,6 +12,7 @@ extern Moveset          moveset_HTM;
 extern Moveset          moveset_URF;
 extern Moveset          moveset_eofb;
 extern Moveset          moveset_drud;
+extern Moveset          moveset_drud_noD;
 extern Moveset          moveset_htr;
 
 void        append_alg(AlgList *l, Alg *alg);
diff --git a/src/steps.c b/src/steps.c
index 85732e7..383acaa 100644
--- a/src/steps.c
+++ b/src/steps.c
@@ -751,7 +751,7 @@ dranyslice_DR = {
         .ready     = check_drud,
         .ready_msg = check_drany_msg,
         .is_valid  = always_valid,
-        .moveset   = &moveset_drud,
+        .moveset   = &moveset_drud_noD,
 
         .detect    = detect_pretrans_drud,
 
@@ -770,7 +770,7 @@ drudslice_drud = {
         .ready     = check_drud,
         .ready_msg = check_dr_msg,
         .is_valid  = always_valid,
-        .moveset   = &moveset_drud,
+        .moveset   = &moveset_drud_noD,
 
         .pre_trans = uf,
 
@@ -789,7 +789,7 @@ drrlslice_drrl = {
         .ready     = check_drud,
         .ready_msg = check_dr_msg,
         .is_valid  = always_valid,
-        .moveset   = &moveset_drud,
+        .moveset   = &moveset_drud_noD,
 
         .pre_trans = rf,
 
@@ -808,7 +808,7 @@ drfbslice_drfb = {
         .ready     = check_drud,
         .ready_msg = check_dr_msg,
         .is_valid  = always_valid,
-        .moveset   = &moveset_drud,
+        .moveset   = &moveset_drud_noD,
 
         .pre_trans = fd,