code: func (c *ChainConfig) IsPetersburg(num *big.Int) bool {
  	return isForked(c.PetersburgBlock, num) || c.PetersburgBlock == nil && isForked(c.ConstantinopleBlock, num)
  }
docs: // IsPetersburg returns whether num is either
  // - equal to or greater than the PetersburgBlock fork block,
  // - OR is nil, and Constantinople is active