```\n    /**\n        Δ_bull = (1 / θ) * F\n        F = {\n@@@         * 0                     if (S < K)\n            * (1 - √(K / Kb)) / K   if (S > Kb)\n            * 1 / K - 1 / √(S * K)  if (K < S < Kb)\n        }\n    */\n    function bullDelta(uint256 k, uint256 kB, uint256 s, uint256 theta) internal pure returns (int256) {\n        SD59x18 delta;\n        if (s <= k) {\n@@@         return 0;\n        }\n```\n