appell4

param appell4 c
array param; array c;
appell4 returns the Lauricella function F_C(a,b, c_1, ..., c_n; x_1,...,x_n)
for the parameter << param >> = [a, c, b_1, ..., b_n].
In case of n=2, the function is called the Appell function F_4.
c = [ generators,  variables ]
Note that for a special set of parameters, the returned differential equation
is not holonomic, e.g., [[1 2 3 4]] appell4 rank ::
Example: [ [1 -4 -2 5 6] ] appell4 rank ::