Sentence examples for a major difficulty is that from inspiring English sources

A major difficulty is that American corporations are governed not only by federal law but also by the rules of the state in which they choose to incorporate.

A major difficulty is that both heat and work (not only heat) are involved.

A major difficulty is that every tumor behaves as an organ that evolves in function of its microenvironment.

Compared to the space homogeneous case, or more in general to the case of splitting based methods, studied in Dimarco Pareschi [7] a major difficulty is that the local Maxwellian equilibrium state change with respect to time and thus needs a proper numerical treatment.

A major difficulty is that the number of available measurements is usually lower than required.

A major difficulty was that, beyond a certain point in most new relationships, condom use could not be sustained.

The major difficulty is that a closed form solution to governing equation of motion is not obtainable.

The major difficulty is that Jan's masterpiece, The Adoration of the Mystic Lamb altarpiece, has a wholly questionable inscription that introduces Hubert van Eyck as its principal master.

One major difficulty is that many of the issues do not break along party lines — they tend instead to force disagreements between industries and their various supporters in Congress.

One major difficulty is that the state observation must only rely on the global system output i.e. the PDE state at the terminal boundary.

The major difficulty is that the EOT is now mainly governed by both the silicon/high-k and the metal gate/high-k interfaces which are not directly scalable.