'split proved rules into alpha and beta chains'

def split_alpha_beta(self):

    rules_alpha = []
    rules_beta = []
    for (a, b) in self.proved_rules:
        if isinstance(a, And):
            rules_beta.append((a, b))
        else:
            rules_alpha.append((a, b))
    return (rules_alpha, rules_beta)
