tuned def. of del and proved preservation of rbt (finally)
(*
Author: Makarius
*)
section \<open>Proof by guessing\<close>
theory Guess
imports Main
begin
notepad
begin
have 1: "\<exists>x. x = x" by simp
from 1 guess ..
from 1 guess x ..
from 1 guess x :: 'a ..
from 1 guess x :: nat ..
have 2: "\<exists>x y. x = x \<and> y = y" by simp
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 :: nat apply - apply (erule exE conjE)+ done
end
end