doc-src/Tutorial/Misc/Fib.thy

HOL/record: shared operations ("more", "fields", etc.) now need to be
always qualified;

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