doc-src/Tutorial/Misc/Itrev.thy

proof by cases and induction on types and sets (used to be specific for HOL);

Itrev = Main +
consts itrev :: 'a list => 'a list => 'a list
primrec
"itrev []     ys = ys"
"itrev (x#xs) ys = itrev xs (x#ys)"
end