canonical 'cases'/'induct' rules for n-tuples (n=3..7)
(really belongs to theory Product_Type, but doesn't work there yet)
Fib = WF_Rel +
consts fib :: nat => nat
recdef fib "measure(%n. n)"
"fib 0 = 0"
"fib 1 = 1"
"fib (Suc(Suc x)) = fib x + fib (Suc x)"
end