Function extern_spec_Instant_duration_since 

pub fn extern_spec_Instant_duration_since(
    self_: &Instant,
    earlier: Instant,
) -> Duration

extern spec for Instant::duration_since

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

terminates

ghost

ensures

self@ > earlier@ ==> result@ > 0

ensures

self@ <= earlier@ ==> result@ == 0