partial_function (tailrec) replaces function (tailrec);
dropped unnecessary domain reasoning;
curried polydivide_aux
Arith = FOL +
classes arith < term
consts "0" :: "'a::arith" ("0")
"1" :: "'a::arith" ("1")
"+" :: "['a::arith,'a] => 'a" (infixl 60)
end