1.2.52 `sm1.restriction'
------------------------

sm1.restriction(I,V,R)
     :  It computes the restriction of I as a D-module to the set
     defined by R.   V is the list of variables.   When the optional
     variable DEGREE=d is given, only the restrictions  from 0 to d are
     computed.   Note that, in case of vector input,  RESTRICTION
     VARIABLES MUST APPEAR FIRST  in the list of variable V. We are
     using wbfRoots to get the roots of  b-functions, so we can use
     only generic weight vector for now.

sm1.restriction(I,V,R | DEGREE=key0)
     : This function allows optional variables   DEGREE

Algorithm:

      T.Oaku and N.Takayama, math.AG/9805006, http://xxx.langl.gov

   Example:
      sm1.restriction([dx^2-x,dy^2-1],[x,y],[y]);

