Reject invalid arguments for SolvableQuotient (#5682)

lib/grppcfp.gi

@@ -808,10 +808,9 @@ local G, epi, tup, lift, i, found, fac, j, p, iso;
             fi;
             Info(InfoSQ,1,"found quotient of size ", Size(G));
         od;
-    fi;
 
     # if <primes> is a list of primes, we have to use try and error
-    if IsList( primes ) and IsInt( primes[1] ) then
+    elif IsList( primes ) and IsInt( primes[1] ) then
         found := true;
         i     := 1;
         while found and i <= Length( primes ) do
@@ -832,10 +831,9 @@ local G, epi, tup, lift, i, found, fac, j, p, iso;
             fi;
             Info(InfoSQ,1,"found quotient of size ", Size(G));
         od;
-    fi;
 
     # if <primes> is an integer it is size we want
-    if IsInt(primes)  then
+    elif IsInt(primes)  then
         if not IsInt(primes/Size(G)) then
           i:=Lcm(primes,Size(G));
           Info(InfoWarning,1,"Added extra factor ",i/primes,
@@ -866,6 +864,8 @@ local G, epi, tup, lift, i, found, fac, j, p, iso;
                 Info(InfoSQ,1,"found quotient of size ", Size(G));
             od;
         od;
+    else
+        Error("<primes> must be either an integer, a list of integers, or a list of integer lists");
     fi;
 
     # this is the result - should be G only with set epimorphism

tst/testinstall/opers/SolvableQuotient.tst

@@ -0,0 +1,33 @@
+gap> START_TEST("SolvableQuotient.tst");
+
+#
+gap> f := FreeGroup( "a", "b", "c", "d" );;
+gap> fp := f / [ f.1^2, f.2^2, f.3^2, f.4^2, f.1*f.2*f.1*f.2*f.1*f.2,
+>  f.2*f.3*f.2*f.3*f.2*f.3*f.2*f.3, f.3*f.4*f.3*f.4*f.3*f.4,
+> f.1^-1*f.3^-1*f.1*f.3, f.1^-1*f.4^-1*f.1*f.4,
+> f.2^-1*f.4^-1*f.2*f.4 ];;
+gap> hom:=EpimorphismSolvableQuotient(fp,300);Size(Image(hom));
+[ a, b, c, d ] -> [ f1*f2, f1*f2, f2*f3, f2 ]
+12
+gap> hom:=EpimorphismSolvableQuotient(fp,[2,3]);Size(Image(hom));
+[ a, b, c, d ] -> [ f1*f2*f4, f1*f2*f6*f8, f2*f3, f2 ]
+1152
+gap> EpimorphismSolvableQuotient(fp,fail);
+Error, <primes> must be either an integer, a list of integers, or a list of in\
+teger lists
+
+#
+gap> SolvableQuotient(fp,300);
+rec( image := <pc group of size 12 with 3 generators>, 
+  imgs := [ f1*f2, f1*f2, f2*f3, f2 ], source := <fp group on the generators 
+    [ a, b, c, d ]> )
+gap> SolvableQuotient(fp,[2,3]);
+rec( image := <pc group of size 1152 with 9 generators>, 
+  imgs := [ f1*f2*f4, f1*f2*f6*f8, f2*f3, f2 ], 
+  source := <fp group on the generators [ a, b, c, d ]> )
+gap> SolvableQuotient(fp,fail);
+Error, <primes> must be either an integer, a list of integers, or a list of in\
+teger lists
+
+#
+gap> STOP_TEST("SolvableQuotient.tst", 10000);