Function verify_chain_rule 

pub fn verify_chain_rule<FJoint, FMarg, FCond>(
    joint: FJoint,
    marginal: FMarg,
    conditional: FCond,
    x: &[u8],
    y: &[u8],
    tolerance: f64,
) -> bool
where
    FJoint: Fn(&[u8], &[u8]) -> f64,
    FMarg: Fn(&[u8]) -> f64,
    FCond: Fn(&[u8], &[u8]) -> f64,

Verify chain rule: H(X,Y) = H(X) + H(Y|X).