Function extern_spec_T_Option_T_and_then 

pub fn extern_spec_T_Option_T_and_then<T, U, F: FnOnce(T) -> Option<U>>(
    self_: Option<T>,
    f: F,
) -> Option<U>

extern spec for Option<T>::and_then

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

requires

match self { None => true, Some(t) => f.precondition((t,)) }

ensures

match self {
    None => result == None,
    Some(t) => f.postcondition_once((t,), result),
}