src/HOL/Induct/Term.thy
 author wenzelm Thu, 22 Dec 2005 00:28:44 +0100 changeset 18461 9125d278fdc8 parent 16417 9bc16273c2d4 child 36862 952b2b102a0a permissions -rw-r--r--
tuned;
```
(*  Title:      HOL/Induct/Term.thy
ID:         \$Id\$
Author:     Stefan Berghofer,  TU Muenchen
*)

header {* Terms over a given alphabet *}

theory Term imports Main begin

datatype ('a, 'b) "term" =
Var 'a
| App 'b "('a, 'b) term list"

text {* \medskip Substitution function on terms *}

consts
subst_term :: "('a => ('a, 'b) term) => ('a, 'b) term => ('a, 'b) term"
subst_term_list ::
"('a => ('a, 'b) term) => ('a, 'b) term list => ('a, 'b) term list"

primrec
"subst_term f (Var a) = f a"
"subst_term f (App b ts) = App b (subst_term_list f ts)"

"subst_term_list f [] = []"
"subst_term_list f (t # ts) =
subst_term f t # subst_term_list f ts"

text {* \medskip A simple theorem about composition of substitutions *}

lemma subst_comp:
"subst_term (subst_term f1 \<circ> f2) t =
subst_term f1 (subst_term f2 t)"
and "subst_term_list (subst_term f1 \<circ> f2) ts =
subst_term_list f1 (subst_term_list f2 ts)"
by (induct t and ts) simp_all

text {* \medskip Alternative induction rule *}

lemma
assumes var: "!!v. P (Var v)"
and app: "!!f ts. list_all P ts ==> P (App f ts)"
shows term_induct2: "P t"
and "list_all P ts"
apply (induct t and ts)
apply (rule var)
apply (rule app)
apply assumption
apply simp_all
done

end
```