function registerOperation(symbol, func) {
  if (!Array.isArray(symbol)) {
    symbol = [symbol.toUpperCase()];
  }
  symbol.forEach(function (s) {
    if (func.isFactory) {
      availableOperators[s] = func(s);
    } else {
      availableOperators[s] = func;
    }
  });
}
Register operator.

@param {String|Array} symbol Symbol to register.
@param {Function} func Logic to register for this symbol.