Function: _'
Section: symbolic_operators
C-Name: deriv
Prototype: GDn
Help: x': derivative of x with respect to the main variable.
Description:
 (gen):gen                      deriv($1,-1)

 (FpX):FpX                      FpX_deriv($1, p)
 (FqX):FqX                      FqX_deriv($1, T, p)
