def tree_observation_probability(state, observation):
    """
    Measurement model for a single Tree element for the LatticeForest.
    Returns a probability of the combination (state, observation).
    """
    measure_correct = 0.9
    measure_wrong = 0.5*(1-measure_correct)
    if state != observation:
        return measure_wrong
    elif state == observation:
        return measure_correct