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(*
Example proof document for Isabelle/Isar Proof General.
$Id$
*)
theory "Example-Xsym" imports Main begin
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 \<and> 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
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