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use std::marker::PhantomData;
/// Type level zero value
pub enum Z {}
/// Type level +1
pub struct S<N: Num>(PhantomData<N>);
/// Type level -1
pub struct P<N: Num>(PhantomData<N>);
/// Type level number
pub trait Num {
/// Next number
type S: Num;
/// Previous number
type P: Num;
/// Convert to value level
fn value() -> usize;
}
impl Num for Z {
type S = S<Z>;
type P = P<Z>;
#[inline]
fn value() -> usize { 0 }
}
impl<N: Num> Num for S<N> {
type S = S<S<N>>;
type P = N;
#[inline]
fn value() -> usize { N::value() + 1 }
}
impl<N: Num> Num for P<N> {
type S = N;
type P = P<P<N>>;
#[inline]
fn value() -> usize { N::value() - 1 }
}