section \<open>Tactic for instantiating existentials\<close>
theory Inst_Existentials
imports Main
begin
text \<open>
Coinduction proofs in Isabelle often lead to proof obligations with nested conjunctions and
existential quantifiers, e.g. @{prop "\<exists>x y. P x y \<and> (\<exists>z. Q x y z)"} .
The following tactic allows instantiating these existentials with a given list of witnesses.
\<close>
ML_file \<open>inst_existentials.ML\<close>
method_setup inst_existentials = \<open>
Scan.lift (Scan.repeat Parse.term) >>
(fn ts => fn ctxt => SIMPLE_METHOD' (Inst_Existentials.tac ctxt
(map (Syntax.read_term ctxt) ts)))
\<close>
end