code: function ungroupOneLevel(compound) {
    let [_all, _op, innerCompound, _cp, multiplier] = compoundGroupRegex.exec(compound)
    let elements = parseElements(innerCompound)
  
    return elements.reduce((accu, elem) => {
      let number = Decimal.mul(elem.count, multiplier)
      let numericPortion = number.toString()
      return accu + `${elem.atom}${numericPortion}`
    }, '')
  }
docs: private