def single_cond_prob_to_str(grid_idx, val, num_indices = 6):
    """Generate the string representing the probability:
    
    Pr(o_i = val)
    
    ex:
    For Pr(o_2 = 1), we'd have the string '21'
    NB we're 1-indexing here
    """
    assert grid_idx >= 1 and grid_idx <= num_indices
    return str(grid_idx) + str(val)