# [isabelle] Something about case rule

First of all , the type declaration:
datatype
('a,'b) val= Var 'a | Const "'b"| Abs 'a "('a,'b) lt"
and
('a,'b) lt= V "('a,'b) val" | App "('a,'b) lt" "('a,'b) lt"
I have declared a case rule
lemma ltnormalcase[case_names Var Const Abs App, cases type]:
assumes "!! x. P (V (Var x))" "!!b. P(V (Const b))" "!! x M. P (V (Abs x
M))"
"!! L M. P (L $ M)" shows "P N"
then how can I use it in the proof context?
I try it in this way (Isar reference Page 85 ,section 4.3.5) :
proof(cases "N" rule:ltnormalcase)
but Isar says:
"
*** Ill-typed instantiation:
*** N :: ('a, 'b) lt
*** At command "proof".
"
Any help?? thanks a lot
YuGang

*This archive was generated by a fusion of
Pipermail (Mailman edition) and
MHonArc.*