Function extern_spec_TryFrom_isize_usize_try_from 

pub fn extern_spec_TryFrom_isize_usize_try_from(
    value: isize,
) -> Result<usize, TryFromIntError>

extern spec for usize::try_from

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

ghost

ensures

match result { Ok(val) => val@ == value@, Err(_) => value@ < 0 }