* Expression importe mal 4x^2
    In [9]: e = Expression("3x + 4x^2 - 1")

    In [10]: print(e)
    3 x + ( 4 x ) ^ 2 - 1

    -> faire un test unitaire dessus
    
*(solved) Render ne met pas les parenthèses là où il faut.

    In [31]: r
    Out[31]: < Polynom [-4, -15, -14]>

    In [35]: print(r)
    -14 * x ^ 2 + -15 x + ( -4 )

    In [36]: r.get_postfix()
    Out[36]: [-14, 'x', 2, '^', '*', -15, 'x', '*', '+', -4, '+']

    In [37]: txt(r.get_postfix())
    Out[37]: '-14 * x ^ 2 + -15 x + ( -4 )'
        

    -> faire un test unitaire dessus

*(solved) Fraction ne simplifie pas correctement 

    In [5]: for i in P.alpha.simplify():
        print(i)
    ...:     
    \frac{ - 2 }{ 2 \times 3 }
    \frac{ -2 }{ 6 }
    \frac{ ( -1 ) \times 2 }{ 3 \times 2 }
    \frac{ -1 }{ 3 }
    \frac{ -2 }{ 6 }

* Opération entre une expression et une fraction ou un Polynom

    In [3]: P = Polynom([1,2,1])

    In [4]: e = Expression("1+2*3")

    In [5]: e + P
    Out[5]: < <class 'pymath.expression.Expression'> [1, 2, 3, '*', '+', < Polynom [1, 2, 1]>, '+'] >

    In [6]: P + e
    ---------------------------------------------------------------------------
    TypeError                                 Traceback (most recent call last)
    <ipython-input-6-ff312ef36cdb> in <module>()
    ----> 1 P + e

    /home/lafrite/scripts/pyMath/pymath/polynom.py in __add__(self, other)
        430         [< <class 'pymath.expression.Expression'> [3, 'x', 2, '^', '*', 2, 'x', '*', '+', 1, '+', 5, 'x', '*', 4, '+', '+'] >, < Polynom [< <class 'pymath.expression.Expression'> [1, 4, '+'] >, < <class 'pymath.expression.Expression'> [2, 5, '+'] >, 3]>, < Polynom [< <class 'pymath.expression.Expression'> [1, 4, '+'] >, < <class 'pymath.expression.Expression'> [2, 5, '+'] >, 3]>]
        431         """
    --> 432         o_poly = self.conv2poly(other)
        433 
        434         n_coef = spe_zip(self._coef, o_poly._coef)

    /home/lafrite/scripts/pyMath/pymath/polynom.py in conv2poly(self, other)
        319             return other
        320         else:
    --> 321             raise ValueError(type(other) + " can't be converted into a polynom")
        322 
        323     def reduce(self):

    TypeError: unsupported operand type(s) for +: 'type' and 'str'

* Parenthèses abhérentes

    In [7]: P = Polynom([-6, 12, -20])

    In [8]: print(P)
    ( - 20 x^{  2 } + 12 x ) - 6