*** Reference example:  ['young', 'myope', 'no', 'reduced', 'none']
['young', 'myope', 'no', 'reduced', 'none'] 0.0
['young', 'myope', 'no', 'normal', 'soft'] 1.0
['young', 'myope', 'yes', 'reduced', 'none'] 1.0
['young', 'myope', 'yes', 'normal', 'hard'] 2.0
['young', 'hypermetrope', 'no', 'reduced', 'none'] 1.0
['young', 'hypermetrope', 'no', 'normal', 'soft'] 2.0
['young', 'hypermetrope', 'yes', 'reduced', 'none'] 2.0
['young', 'hypermetrope', 'yes', 'normal', 'hard'] 3.0
['pre-presbyopic', 'myope', 'no', 'reduced', 'none'] 1.0
['pre-presbyopic', 'myope', 'no', 'normal', 'soft'] 2.0
['pre-presbyopic', 'myope', 'yes', 'reduced', 'none'] 2.0
['pre-presbyopic', 'myope', 'yes', 'normal', 'hard'] 3.0
['pre-presbyopic', 'hypermetrope', 'no', 'reduced', 'none'] 2.0
['pre-presbyopic', 'hypermetrope', 'no', 'normal', 'soft'] 3.0
['pre-presbyopic', 'hypermetrope', 'yes', 'reduced', 'none'] 3.0
['pre-presbyopic', 'hypermetrope', 'yes', 'normal', 'none'] 4.0
['presbyopic', 'myope', 'no', 'reduced', 'none'] 1.0
['presbyopic', 'myope', 'no', 'normal', 'none'] 2.0
['presbyopic', 'myope', 'yes', 'reduced', 'none'] 2.0
['presbyopic', 'myope', 'yes', 'normal', 'hard'] 3.0
['presbyopic', 'hypermetrope', 'no', 'reduced', 'none'] 2.0
['presbyopic', 'hypermetrope', 'no', 'normal', 'soft'] 3.0
['presbyopic', 'hypermetrope', 'yes', 'reduced', 'none'] 3.0
['presbyopic', 'hypermetrope', 'yes', 'normal', 'none'] 4.0
