Allow ParallelSort on lists without IsDenseList

This was already allowed in Sort. While Sort and ParallelSort
both fail with an error if given a non-dense lists, there can
exists lists which are dense but do not have the filter IsDenseList

lib/list.gd

@@ -1786,14 +1786,14 @@ DeclareGlobalFunction( "PermListList" );
 ##  <#/GAPDoc>
 ##
 DeclareOperation( "SortParallel",
-    [ IsDenseList and IsMutable, IsDenseList and IsMutable ] );
+    [ IsList and IsMutable, IsList and IsMutable ] );
 DeclareOperation( "SortParallel",
-    [ IsDenseList and IsMutable, IsDenseList and IsMutable, IsFunction ] );
+    [ IsList and IsMutable, IsList and IsMutable, IsFunction ] );
 
 DeclareOperation( "StableSortParallel",
-    [ IsDenseList and IsMutable, IsDenseList and IsMutable ] );
+    [ IsList and IsMutable, IsList and IsMutable ] );
 DeclareOperation( "StableSortParallel",
-    [ IsDenseList and IsMutable, IsDenseList and IsMutable, IsFunction ] );
+    [ IsList and IsMutable, IsList and IsMutable, IsFunction ] );
 
 
 #############################################################################

lib/list.gi

@@ -2460,15 +2460,15 @@ InstallMethod( SortingPerm,
 #M  SortParallel( <list>, <list2> ) . . . . . . .  sort two lists in parallel
 ##
 InstallMethod( SortParallel,
-    "for two dense and mutable lists",
-    [ IsDenseList and IsMutable,
-      IsDenseList and IsMutable ],
+    "for two mutable lists",
+    [ IsList and IsMutable,
+      IsList and IsMutable ],
     SORT_PARA_LIST );
 
 InstallMethod( StableSortParallel,
-    "for two dense and mutable lists",
-    [ IsDenseList and IsMutable,
-      IsDenseList and IsMutable ],
+    "for two mutable lists",
+    [ IsList and IsMutable,
+      IsList and IsMutable ],
     STABLE_SORT_PARA_LIST );
 
 #############################################################################
@@ -2494,16 +2494,16 @@ InstallMethod( StableSortParallel,
 #M  SortParallel( <list>, <list2>, <func> )
 ##
 InstallMethod( SortParallel,
-    "for two dense and mutable lists, and function",
-    [ IsDenseList and IsMutable,
-      IsDenseList and IsMutable,
+    "for mutable lists, and function",
+    [ IsList and IsMutable,
+      IsList and IsMutable,
       IsFunction ],
     SORT_PARA_LIST_COMP );
 
 InstallMethod( StableSortParallel,
-    "for two dense and mutable lists, and function",
-    [ IsDenseList and IsMutable,
-      IsDenseList and IsMutable,
+    "for two mutable lists, and function",
+    [ IsList and IsMutable,
+      IsList and IsMutable,
       IsFunction ],
     STABLE_SORT_PARA_LIST_COMP );
 

tst/testinstall/objlist.tst

@@ -60,6 +60,19 @@ gap> IsSet(a);
 true
 gap> x;
 [ 2, 10, "cheese" ]
+gap> SortBy(a, {z} -> z);
+gap> a;
+[ 2, 10, "cheese" ]
+gap> SortParallel([3,2,1],a);
+gap> a;
+[ "cheese", 10, 2 ]
+gap> l := [1,2,3];
+[ 1, 2, 3 ]
+gap> SortParallel(a,l);
+gap> a;
+[ 2, 10, "cheese" ]
+gap> l;
+[ 3, 2, 1 ]
 gap> Unbind(x[2]);
 gap> a;
 [ 2,, "cheese" ]