def SEQUENCE(self, ast):
    if (not ast.terms):
        return model.Empty()
    elif (len(ast.terms) < 2):
        return ast.terms[0]
    else:
        return model.Sequence(ast.terms)
def SEQUENCE(self, ast):
    if (not ast.terms):
        return model.Empty()
    elif (len(ast.terms) < 2):
        return ast.terms[0]
    else:
        return model.Sequence(ast.terms)