
diff -r b93d1b3ee300 -r bd91b77c4cd6 src/HOL/RealVector.thy
--- a/src/HOL/RealVector.thy	Sun Aug 28 16:28:07 2011 -0700
+++ b/src/HOL/RealVector.thy	Sun Aug 28 20:56:49 2011 -0700
@@ -1191,4 +1191,17 @@
   shows "x \<noteq> y \<longleftrightarrow> (\<exists>U. open U \<and> ~(x\<in>U \<longleftrightarrow> y\<in>U))"
   using t0_space[of x y] by blast
 
+text {* A perfect space is a topological space with no isolated points. *}
+
+class perfect_space = topological_space +
+  assumes not_open_singleton: "\<not> open {x}"
+
+instance real_normed_algebra_1 \<subseteq> perfect_space
+proof
+  fix x::'a
+  show "\<not> open {x}"
+    unfolding open_dist dist_norm
+    by (clarsimp, rule_tac x="x + of_real (e/2)" in exI, simp)
+qed
+
 end




