1 files changed, 40 insertions, 5 deletions

diff --git a/src/steps.c b/src/steps.c
index 6754d22..85732e7 100644
--- a/src/steps.c
+++ b/src/steps.c
@@ -38,6 +38,7 @@ static int              estimate_nxoptlike(DfsArg *arg, PruneData *pd);
 
 static bool             always_valid(Alg *alg);
 static bool             validate_singlecw_ending(Alg *alg);
+static bool             validate_htr_qt(Alg *alg);
 
 /* Pre-transformation detectors **********************************************/
 
@@ -407,7 +408,7 @@ cornershtr_HTM = {
         .is_done   = check_cornershtr,
         .estimate  = estimate_cornershtr_HTM,
         .ready     = NULL,
-        .is_valid  = validate_singlecw_ending,
+        .is_valid  = validate_htr_qt,
         .moveset   = &moveset_HTM,
 
         .pre_trans = uf,
@@ -903,7 +904,7 @@ htr_any = {
         .estimate  = estimate_htr_drud,
         .ready     = check_drud,
         .ready_msg = check_drany_msg,
-        .is_valid  = validate_singlecw_ending,
+        .is_valid  = validate_htr_qt,
         .moveset   = &moveset_drud,
 
         .detect    = detect_pretrans_drud,
@@ -922,7 +923,7 @@ htr_drud = {
         .estimate  = estimate_htr_drud,
         .ready     = check_drud,
         .ready_msg = check_dr_msg,
-        .is_valid  = validate_singlecw_ending,
+        .is_valid  = validate_htr_qt,
         .moveset   = &moveset_drud,
 
         .pre_trans = uf,
@@ -941,7 +942,7 @@ htr_drrl = {
         .estimate  = estimate_htr_drud,
         .ready     = check_drud,
         .ready_msg = check_dr_msg,
-        .is_valid  = validate_singlecw_ending,
+        .is_valid  = validate_htr_qt,
         .moveset   = &moveset_drud,
 
         .pre_trans = rf,
@@ -960,7 +961,7 @@ htr_drfb = {
         .estimate  = estimate_htr_drud,
         .ready     = check_drud,
         .ready_msg = check_dr_msg,
-        .is_valid  = validate_singlecw_ending,
+        .is_valid  = validate_htr_qt,
         .moveset   = &moveset_drud,
 
         .pre_trans = fd,
@@ -1599,6 +1600,40 @@ validate_singlecw_ending(Alg *alg)
         return nor && inv;
 }
 
+static bool
+validate_htr_qt(Alg *alg)
+{
+        int i, lastqt, lastqt_n, lastqt_i;
+        Move m, b;
+
+        if (!validate_singlecw_ending(alg))
+                return false;
+
+        lastqt_n = lastqt_i = -1;
+        for (i = 0; i < alg->len; i++) {
+                m = alg->move[i];
+                b = base_move(m);
+                if (m == b+1)
+                        continue;
+                if (alg->inv[i] && lastqt_i == -1)
+                        lastqt_i = i;
+                if (!alg->inv[i])
+                        lastqt_n = i;
+        }
+        lastqt = lastqt_n == -1 ? lastqt_i : lastqt_n;
+
+        for (i = 0; i < alg->len; i++) {
+                m = alg->move[i];
+                b = base_move(m);
+                if (m == b+1 || i == lastqt)
+                        continue;
+                if (b == D || b == L || b == B)
+                        return false;
+        }
+
+        return true;
+}
+
 /* Pre-transformation detectors **********************************************/
 
 static int