simplify method
Implementation
Unit simplify() {
var elements =
_elements.where((e) => e.pow.dividend != 0 || e.pow.divisor == 0);
if (elements.length == 1) {
if (elements.first.pow == RationalNumber(1, 1)) {
return elements.first.base;
}
}
return ProductUnit._(elements.toList());
}