Fix Mandarins

Author: ssiccha

gap/base/recognition.gi

@@ -580,11 +580,16 @@ InstallGlobalFunction( RecogniseGeneric,
             fi;
         fi;
 
-        # TODO: store the mandarins and their SLPs?
+        # TODO: store the mandarin SLPs here. Make sure, to only write when succesful.
         # check mandarins now
         for x in mandarins do
             s := SLPforElement(ri, x);
             if s = fail then
+                # TODO: with the master branch rewriting the gens as slps never
+                # fails. at least we never enter  a second iteration of the
+                # "recognise image" loop.
+                Info(InfoRecog, 2,
+                     "Enter Mandarin crisis, backtrack to the last safe node.");
                 return MANDARIN_CRISIS;
             fi;
         od;
@@ -608,6 +613,9 @@ InstallGlobalFunction( RecogniseGeneric,
     # fails, then somewhere higher up in the recognition tree, a kernel must
     # have been too small.
     if ForAny(mandarins, x->not ValidateHomomInput(ri, x)) then
+        Info(InfoRecog, 2,
+             "ValidateHomomInput for a mandarin failed,",
+             " backtracking to the last safe node.");
         return MANDARIN_CRISIS;
     fi;
     # Compute the mandarins of the factor
@@ -655,6 +663,9 @@ InstallGlobalFunction( RecogniseGeneric,
                   factorMandarins,
                   IsSafeForMandarins(ri));
         Remove(depthString);
+        PrintTreePos("F",depthString,H);
+        SetImageRecogNode(ri,rifac);
+        SetParentRecogNode(rifac,ri);
         if not IsReady(rifac) then
             # IsReady was not set, thus abort the whole computation.
             if InfoLevel(InfoRecog) = 1 and depth = 0 then Print("\n"); fi;
@@ -665,9 +676,6 @@ InstallGlobalFunction( RecogniseGeneric,
             # tree, a kernel must have been too small.
             return MANDARIN_CRISIS;
         fi;
-        PrintTreePos("F",depthString,H);
-        SetImageRecogNode(ri,rifac);
-        SetParentRecogNode(rifac,ri);
 
         if IsMatrixGroup(H) then
             Info(InfoRecog,2,"Back from image (depth=",depth,
@@ -723,11 +731,8 @@ InstallGlobalFunction( RecogniseGeneric,
         x := mandarins[i];
         y := factorMandarins[i];
         s := SLPforElement(rifac, y);
-        # TODO: these SLPs should be stored when they are computed for the
-        # first time.
-        if s = fail then
-            Error("TODO: no SLP for factor");
-        fi;
+        # TODO: These SLPs should be stored when they are computed for the
+        # first time. In particular, they can't be fail.
         z := ResultOfStraightLineProgram(s, pregensfac(ri));
         if not ri!.isequal(x, z) then
             Add( kernelMandarins, x / z );
@@ -740,12 +745,15 @@ InstallGlobalFunction( RecogniseGeneric,
         RECOG_HandleSpecialCaseKernelTrivialAndMarkedForImmediateVerification(ri);
     fi;
     if IsEmpty(gensN(ri)) and not IsEmpty(kernelMandarins) then
-        # We found out that N is the trivial group, but the mandarins disagree!
+        Info(InfoRecog, 2, "Kernel is trivial although mandarins disagree.");
         # We handle this in the same way as if recognition of the
         # kernel returned a MANDARIN_CRISIS.
         if not IsSafeForMandarins(ri) then
+            Info(InfoRecog, 2, "Backtrack to the last safe node.");
             return MANDARIN_CRISIS;
         else
+            Info(InfoRecog, 2,
+                 "Handle the mandarin crisis at depth=", depth, ".");
             if not TryToEnlargeKernelGeneratingSetAndUpdateSLPsDuringMandarinCrisis(ri) then
                 # TODO: discard and re-recognise the image.
                 ErrorNoReturn("TODO");
@@ -784,35 +792,34 @@ InstallGlobalFunction( RecogniseGeneric,
                                    kernelMandarins,
                                    # TODO: extend this such that riker can also
                                    # be IsSafeForMandarins, if the responsible
-                                   # findgensNmeth is guaranteed to feed the
+                                   # findgensNmeth is guaranteed to find the
                                    # generators for the whole kernel.
                                    false);
         Remove(depthString);
+        PrintTreePos("K",depthString,H);
+        SetKernelRecogNode(ri,riker);
+        SetParentRecogNode(riker,ri);
+        Info(InfoRecog,2,"Back from kernel (depth=",depth,").");
         if riker = MANDARIN_CRISIS then
             # According to the mandarins, there was an error in the kernel
             # generation of the current node or higher up in the recognition
             # tree.
+            Info(InfoRecog, 2, "Enter mandarin crisis.");
             if not IsSafeForMandarins(ri) then
-                # Backtrack to the first safe node on the way to the root.
+                Info(InfoRecog, 2, "Backtrack to the last safe node.");
                 return MANDARIN_CRISIS;
             fi;
+            Info(InfoRecog, 2,
+                 "Handle the mandarin crisis at depth=", depth, ".");
             # We are the first safe node on the way to the root and thus need to
             # handle the crisis ourselves.
-            enlargeKernelSuccess :=
-                TryToEnlargeKernelGeneratingSetAndUpdateSLPsDuringMandarinCrisis(ri);
-            if not enlargeKernelSuccess then
+            if not TryToEnlargeKernelGeneratingSetAndUpdateSLPsDuringMandarinCrisis(ri) then
                 # TODO: discard and re-recognise the image.
                 ErrorNoReturn("TODO");
             fi;
             # This restarts the loop, since mandarinSuccess is false.
             continue;
-        else
-            mandarinSuccess := true;
         fi;
-        PrintTreePos("K",depthString,H);
-        SetKernelRecogNode(ri,riker);
-        SetParentRecogNode(riker,ri);
-        Info(InfoRecog,2,"Back from kernel (depth=",depth,").");
 
         if not IsReady(riker) then
             # IsReady is not set, thus the whole computation aborts.
@@ -830,12 +837,16 @@ InstallGlobalFunction( RecogniseGeneric,
             fi;
         fi;
         for x in kernelMandarins do
-            if SLPforElement(ri, x) = fail then
+            if SLPforElement(riker, x) = fail then
+                Info(InfoRecog, 2, "Enter mandarin crisis.");
                 # We handle this in the same way as if recognition of the
                 # kernel returned a MANDARIN_CRISIS.
                 if not IsSafeForMandarins(ri) then
+                    Info(InfoRecog, 2, "Backtrack to the last safe node.");
                     return MANDARIN_CRISIS;
                 fi;
+                Info(InfoRecog, 2,
+                     "Handle the mandarin crisis at depth=", depth, ".");
                 if not TryToEnlargeKernelGeneratingSetAndUpdateSLPsDuringMandarinCrisis(ri) then
                     # TODO: discard and re-recognise the image.
                     ErrorNoReturn("TODO");
@@ -844,6 +855,7 @@ InstallGlobalFunction( RecogniseGeneric,
                 continue;
             fi;
         od;
+        mandarinSuccess := true;
     until mandarinSuccess and immediateVerificationSuccess;
 
     SetNiceGens(ri,Concatenation(pregensfac(ri), NiceGens(riker)));