Neutrality proved difficult to maintain, though.
But this distinction has proved difficult to maintain.
But that success may prove difficult to maintain, depending in large part on decisions the Texas Legislature will make this year to confront a budget shortfall that could reach $20 billion or more.
But design runs a lot deeper and, with the growing portfolio of products, Google's philosophy of keeping it simple with minimalism is proving difficult to maintain.
By 1849 however, it proved difficult to maintain the old system and in that year the metric system became the legal system of measure in Spain.
Further complicating things, parts for the theatre's Edison and Simplex projectors were difficult to come by at the best of times, and the complex machines proved difficult to maintain.
That sort of restraint, however, could prove difficult to maintain in New York, where Sanders will be under constant attack from Clinton, her surrogates and even the state's famously feisty news media.
Much effort and expense has been applied to install and monitor such plots, yet they often prove difficult to maintain over time.
The toxic dinoflagellate Gambierdiscus has also proved difficult to maintain in culture; it grows slowly and does not attain high biomass [ 66- 68].
