canonical 'cases'/'induct' rules for n-tuples (n=3..7)
(really belongs to theory Product_Type, but doesn't work there yet)
theory ToyList = PreList:
datatype 'a list = Nil ("[]")
| Cons 'a "'a list" (infixr "#" 65)
consts app :: "'a list => 'a list => 'a list" (infixr "@" 65)
rev :: "'a list => 'a list"
primrec
"[] @ ys = ys"
"(x # xs) @ ys = x # (xs @ ys)"
primrec
"rev [] = []"
"rev (x # xs) = (rev xs) @ (x # [])"