['The', 'approach', 'hereby', 'presented', 'is', 'of', 'remarkable', 'simplicity', ',', 'has', 'been', 'successfully', 'applied', 'to', 'spin', '\xa0 ', '[', '17–19,14,16', ']', 'and', 'macroscopic', 'thermodynamic', 'systems', '\xa0 ', '[', '20,15', ']', 'and', 'can', 'be', 'further', 'extended', 'to', 'include', 'the', 'larger', 'class', 'of', 'models', 'admitting', 'partition', 'functions', 'of', 'the', 'form', '(', '4', ')', 'to', 'be', 'used', 'to', 'extend', 'to', 'the', 'critical', 'region', 'general', 'equations', 'of', 'state', 'of', 'the', 'form', '(', '7', ')', 'including', 'a', 'class', 'virial', 'expansions', '.']