Function extern_spec_u128_checked_add 

pub fn extern_spec_u128_checked_add(self_: u128, rhs: u128) -> Option<u128>

extern spec for u128::checked_add

This is not a real function: its only use is for documentation.

terminates

ghost

ensures

(result == None)
                    == ((self@ $op rhs@) < $type::MIN@ || (self@ $op rhs@) > $type::MAX@)

ensures

forall<r: $type> result == Some(r) ==> r@ == (self@ $op rhs@)