TypeError: 'sage.rings.integer.Integer' object is not callable

edit

I tried to enter into notebook:

a=-2

(-((a-1)^2)-((-a-8)(2(a-1))))/((a-1)^4)

And I obtained error

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "_sage_input_13.py", line 10, in <module> exec compile(u'open("___code___.py","w").write("# -- coding: utf-8 --\n" + _support_.preparse_worksheet_cell(base64.b64decode("KC0oKGEtMSleMiktKCgtYS04KSgyKGEtMSkpKSkvKChhLTEpXjQp"),globals())+"\n"); execfile(os.path.abspath("___code___.py")) File "", line 1, in <module> File "/tmp/tmpF91cWI/___code___.py", line 3, in <module> exec compile(u'(-((a-_sage_const_1 )_sage_const_2 )-((-a-_sage_const_8 )(_sage_const_2 (a-_sage_const_1 ))))/((a-_sage_const_1 )_sage_const_4 ) File "", line 1, in <module> TypeError: 'sage.rings.integer.Integer' object is not callable