1. I use your previous reply on V_G derive on other characteristic function, but most are undefined
or complicated solution or can not evaluate, why?
for example
charc := 1+i*X/(i*X-1);
int(exp(-I*X*u)*charc, X = -infinity .. infinity);
it got this complicated thing
piecewise(Im(1/i) = 0, undefined, int(exp(-I*X*u)*(1+i*X/(i*X-1)), X = -infinity .. infinity, method = _UNEVAL))
Density := int(exp(-I*X*u)*charc, X = -infinity .. infinity);