fix the action of WreathProdElem on MatElem

mul! is not correct for NmodRing??

groups/speciallinear.jl

@@ -10,8 +10,8 @@ struct SpecialLinearGroup <: SymmetrizedGroup
         if p == 0
             G = MatrixSpace(Nemo.ZZ, n, n)
         else
-            F, a = FiniteField(p, 1, "a")
-            G = MatrixSpace(F, n, n)
+            R = Nemo.NmodRing(UInt(p))
+            G = MatrixSpace(R, n, n)
         end
         return new(args, G)
     end
@@ -83,9 +83,7 @@ function (g::WreathProductElem)(A::MatElem)
     G = matrix_emb(g.n, g_inv.p)
     G_inv = matrix_emb(g_inv.n, g.p)
     M = parent(A)
-    res = M(G_inv)
-    Nemo.mul!(res, A, res)
-    return Nemo.mul!(res, M(G), res)
+    return M(G)*A*M(G_inv)
 end
 
 import Base.*