def _calculate_emissions(emission_probs):
    """Calculate which symbols can be emitted in each state
    """
    # loop over all of the state-symbol duples, mapping states to
    # lists of emitted symbols
    emissions = dict()
    for state, symbol in emission_probs:
        try:
            emissions[state].append(symbol)
        except KeyError:
            emissions[state] = [symbol]

    return emissions