Universal string and small N = 4 superstring

It was previously shown that most of the superstrings can be obtained from those with higher world-sheet supersymmetry as spontaneously broken phases. In this paper, we show that the small N = 4 superstring, which was left out of this hierarchy of the universal string, can be obtained from the large N = 4 string. We also show that the N = 2 string is a special vacuum of the small N = 4 string. Thus all the known superstring theories can be derived from a universal string by spontaneous breakdown of supersymmetry.