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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add(self, parent, child):
 """Add a pair of boolean sensors. Parent depends on child. Parameters parent : boolean instance of :class:`katcp.Sensor` The sensor that depends on child. child : boolean instance of :class:`katcp.Sensor` The sensor parent depends on. """

        if parent not in self:
            if parent.stype != "boolean":
                raise ValueError("Parent sensor %r is not boolean" % child)
            self._parent_to_not_ok[parent] = set()
        if child not in self:
            if child.stype != "boolean":
                raise ValueError("Child sensor %r is not booelan" % child)
            self._parent_to_not_ok[child] = set()
        self.add_links(parent, (child,))