def apply(dfg):
    """
    Computes a causal graph based on a directly follows graph according to the alpha miner

    Parameters
    ----------
    dfg: :class:`dict` directly follows relation, should be a dict of the form (activity,activity) -> num of occ.

    Returns
    -------
    causal_relation: :class:`dict` containing all causal relations as keys (with value 1 indicating that it holds)
    """
    causal_alpha = {}
    for f, t in dfg:
        if dfg[f, t] > 0:
            if (t, f) not in dfg:
                causal_alpha[f, t] = 1
            elif dfg[t, f] == 0:
                causal_alpha[f, t] = 1
    return causal_alpha
