(self)
return self._ker
r"""
        Compute the kernel of ``self``.

        That is, if ``self`` is the homomorphism `\phi: M \to N`, then compute
        `ker(\phi) = \{x \in M | \phi(x) = 0\}`.  This is a submodule of `M`.

        >>> from sympy import QQ
        >>> from sympy.abc import x
        >>> from sympy.polys.agca import homomorphism

        >>> F = QQ.old_poly_ring(x).free_module(2)
        >>> homomorphism(F, F, [[1, 0], [x, 0]]).kernel()
        <[x, -1]>
r"""
        Compute the kernel of ``self``.
r Compute the kernel of self .
def kernel(self):
        r"""
        Compute the kernel of ``self``.

        That is, if ``self`` is the homomorphism `\phi: M \to N`, then compute
        `ker(\phi) = \{x \in M | \phi(x) = 0\}`.  This is a submodule of `M`.

        >>> from sympy import QQ
        >>> from sympy.abc import x
        >>> from sympy.polys.agca import homomorphism

        >>> F = QQ.old_poly_ring(x).free_module(2)
        >>> homomorphism(F, F, [[1, 0], [x, 0]]).kernel()
        <[x, -1]>
        """
        if self._ker is None:
            self._ker = self._kernel()
        return self._ker
def kernel ( self ) : if self . _ker is None : self . _ker = self . _kernel ( ) return self . _ker