canonical 'cases'/'induct' rules for n-tuples (n=3..7)
(really belongs to theory Product_Type, but doesn't work there yet)
Itrev = Main +
consts itrev :: 'a list => 'a list => 'a list
primrec
"itrev [] ys = ys"
"itrev (x#xs) ys = itrev xs (x#ys)"
end