Function canrun::state::constraints::resolve_2

pub fn resolve_2<'a, A, B, D>(
    a: &Val<A>, 
    b: &Val<B>, 
    state: &State<'a, D>
) -> Result<(Rc<A>, Rc<B>), VarWatch> where
    A: Debug,
    B: Debug,
    D: DomainType<'a, A> + DomainType<'a, B>, 

Resolve two Vals or return an Err(VarWatch) in a Constraint.