fix a bug in galois_projection

Modularity.m

@@ -82,10 +82,12 @@ intrinsic galois_projection(R1 :: FldNum[FldRat],
 
     // subgroup of gal2 corresponding to R1
     gal_R1 := Stabilizer(gal2, {1,p});
-    assert #gal_R1 eq 2*#gal_R2;
+    if gal_R1 eq gal_R2 then
+      continue;
+    end if;
 
     // subgroup of gal2 corresponding to R (Galois closure of R1)
-    gal_R := &meet Conjugates(gal2, gal_R1);
+    gal_R := Core(gal2, gal_R1);
 
     // Check that {1, p} are really conjugates
     if #gal2 eq #gal_R * #gal then
@@ -93,6 +95,8 @@ intrinsic galois_projection(R1 :: FldNum[FldRat],
     end if;
 
   end for;
+  assert #gal_R1 eq 2*#gal_R2;
+  assert #gal2 eq #gal_R * #gal;
 
   // proj : gal2 --> gal1 
   proj, gal1 := CosetAction(gal2, gal_R1);