: Macro Operators
[string1 string2] ring_of_differential_difference operators
This command is used to define a ring of differential-difference operators
with the macros define_ring, weight_vector and elimination_order.
string1 is a set of variables for differential operators.
string2 is a set of variables for difference operators.
The user cannot use the variable names h, e, H and E.
cf. show_ring, system_variable --- CurrentRing
Example: [[(x,y) (s)] ring_of_differential_difference_operators
[[(Es) 1] [(s) 1]] weight_vector 0] define_ring
Dx and Dy are corresponding differential operators to the
space variables x and y. Try show_ring to see the commutation