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+(*
+      Example proof document for Isabelle/Isar Proof General.
+   
+      $Id$
+*)
+
+theory Example = Main:
+
+text {* Proper proof text -- \textit{naive version}. *}
+
+theorem and_comms: "A \<and> B \<longrightarrow> B \<and> A"
+proof
+  assume "A \<and> B"
+  then show "B \<and> A"
+  proof
+    assume B and A
+    then
+   show ?thesis ..
+ qed
+qed
+
+
+text {* Proper proof text -- \textit{advanced version}. *}
+
+theorem "A \<and> B \<longrightarrow> B \<and> A"
+proof
+  assume "A & B"
+  then obtain B and A ..
+  then show "B \<and> A" ..
+qed
+
+
+text {* Unstructured proof script. *}
+
+theorem "A \<and> B \<longrightarrow> B \<and> A"
+  apply (rule impI)
+  apply (erule conjE)
+  apply (rule conjI)
+  apply assumption
+  apply assumption
+done
+
+end