pub fn relate_args_with_variances<I, R>(
relation: &mut R,
variances: <I as Interner>::VariancesOf,
a_args: <I as Interner>::GenericArgs,
b_args: <I as Interner>::GenericArgs,
) -> Result<<I as Interner>::GenericArgs, TypeError<I>>where
I: Interner,
R: TypeRelation<I>,