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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 permissions(self, addr, permissions=None):
 """ Retrieve the permissions of the page at address `addr`. :param addr: address to get the page permissions :param permissions: Integer or BVV to optionally set page permissions to :return: AST representing the permissions on the page """

        out = self.mem.permissions(addr, permissions)
        # if unicorn is in play and we've marked a page writable, it must be uncached
        if permissions is not None and self.state.solver.is_true(permissions & 2 == 2):
            if self.state.has_plugin('unicorn'):
                self.state.unicorn.uncache_page(addr)
        return out