src/Doc/Locales/Examples2.thy

more Haskell operations;

theory Examples2
imports Examples
begin
  interpretation %visible int: partial_order "(\<le>) :: [int, int] \<Rightarrow> bool"
    rewrites "int.less x y = (x < y)"
  proof -
    txt \<open>\normalsize The goals are now:
      @{subgoals [display]}
      The proof that~@{text \<le>} is a partial order is as above.\<close>
    show "partial_order ((\<le>) :: int \<Rightarrow> int \<Rightarrow> bool)"
      by unfold_locales auto
    txt \<open>\normalsize The second goal is shown by unfolding the
      definition of @{term "partial_order.less"}.\<close>
    show "partial_order.less (\<le>) x y = (x < y)"
      unfolding partial_order.less_def [OF \<open>partial_order (\<le>)\<close>]
      by auto
  qed

text \<open>Note that the above proof is not in the context of the
  interpreted locale.  Hence, the premise of @{text
  "partial_order.less_def"} is discharged manually with @{text OF}.
\<close>
end