FLink is used to evaluate expressions externally from Mathematica in the Fermat program.
One of the most powerful features of Fermat is the fast evaluation of the GCD - the greatest common divisor.
Thus one can speed-up the evaluations in Mathematica: instead of calling Together, one should transform the expression into a string, call the external FEval function and again convert the result into an expression.
Currently one is required to list the variables at the initialization. This restriction is to be removed in December when a variable auto declare option is introduced into Fermat.
The variables should be all low-case.
It is recomended to close the FLink from Mathematica, otherwise the Fermat process might get hanged and not killed automatically after you exit Mathematica.