[isabelle] basic example causes error message


I have installed the official Isabelle release, and tried the
following example from Programming and Proving:

theory MyList
imports Main
datatype ’a list = Nil | Cons ’a "’a list"
fun app :: "’a list => ’a list => ’a list" where
"app Nil ys = ys" |
"app (Cons x xs) ys = Cons x (app xs ys)"
fun rev :: "’a list => ’a list" where
"rev Nil = Nil" |
"rev (Cons x xs) = app (rev xs) (Cons x Nil)"
value "rev(Cons True (Cons False Nil))"

now, at the datatype declaration jedit shows an error sign and the output says

Outer syntax error: name declaration expected,
but bad input ’a was found

What is the problem here?

- Gergely

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