more thorough treatment of build prefs, guarded by system option "build_through": avoid accidental rebuild of HOL etc.;
(* Title: Pure/ex/Guess_Examples.thy
Author: Makarius
*)
section \<open>Proof by wild guessing\<close>
theory Guess_Examples
imports "Pure-Examples.Higher_Order_Logic" Guess
begin
typedecl t
instance t :: type ..
notepad
begin
have 1: "\<exists>x :: 'a. x = x" by (intro exI refl)
from 1 guess ..
from 1 guess x ..
from 1 guess x :: 'a ..
from 1 guess x :: t ..
have 2: "\<exists>(x::'c) (y::'d). x = x \<and> y = y" by (intro exI conjI refl)
from 2 guess apply - apply (erule exE conjE)+ done
from 2 guess x apply - apply (erule exE conjE)+ done
from 2 guess x y apply - apply (erule exE conjE)+ done
from 2 guess x :: 'a and y :: 'b apply - apply (erule exE conjE)+ done
from 2 guess x y :: t apply - apply (erule exE conjE)+ done
end
end