declare module "black-scholes" {
  export function blackScholes(
    forwardPrice: number,
    strike: number,
    timeFractionOfYear: number,
    impliedVol: number,
    riskFreeRate: number,
    callPut: "call" | "put"
  ): number;
  export function stdNormCDF(x: number): number;
  export function getW(
    s: number,
    k: number,
    t: number,
    v: number,
    r: number
  ): number;
}