def remove(self, elem):
        """Remove a requirement.

        :param elem: a string or :class:`Requirement` instance.
        """
        if isinstance(elem, text_type):
            for requirement in self:
                if requirement.package == elem:
                    return super(Requirements, self).remove(requirement)
        return super(Requirements, self).remove(elem)
def setSSS(self, lenp3, lenp1, lenp2):
        self.lenp3 = lenp3
        self.lenp1 = lenp1
        self.lenp2 = lenp2
        self.ap1 = math.acos(((self.lenp2 * self.lenp2 + self.lenp3 * self.lenp3) - self.lenp1 * self.lenp1) / (2* self.lenp2 * self.lenp3))
        self.ap2 = math.acos(((self.lenp1 * self.lenp1 + self.lenp3 * self.lenp3) - self.lenp2 * self.lenp2) / (2* self.lenp1 * self.lenp3))
        self.ap3 = math.acos(((self.lenp1 * self.lenp1 + self.lenp2 * self.lenp2) - self.lenp3 * self.lenp3) / (2* self.lenp1 * self.lenp2))