# Singular

##### 7.5.20.0. extendWeyl
Procedure from library `dmodloc.lib` (see dmodloc_lib).

Usage:
extendWeyl(S); S string or list of strings

Assume:
The basering is the n-th Weyl algebra over a field of characteristic 0 and for all 1<=i<=n the identity
var(i+n)*var(i)=var(i)*var(i+1)+1 holds, i.e. the sequence of variables is given by x(1),...,x(n),D(1),...,D(n), where D(i) is the differential operator belonging to x(i).

Return:
ring, Weyl algebra extended by vars given by S

Example:
 ```LIB "dmodloc.lib"; ring @D2 = 0,(x,y,Dx,Dy),dp; def D2 = Weyl(); setring D2; def D3 = extendWeyl("t"); setring D3; D3; ==> // coefficients: QQ ==> // number of vars : 6 ==> // block 1 : ordering dp ==> // : names t x y Dt Dx Dy ==> // block 2 : ordering C ==> // noncommutative relations: ==> // Dtt=t*Dt+1 ==> // Dxx=x*Dx+1 ==> // Dyy=y*Dy+1 list L = "u","v"; def D5 = extendWeyl(L); setring D5; D5; ==> // coefficients: QQ ==> // number of vars : 10 ==> // block 1 : ordering dp ==> // : names u v t x y Du Dv Dt Dx Dy ==> // block 2 : ordering C ==> // noncommutative relations: ==> // Duu=u*Du+1 ==> // Dvv=v*Dv+1 ==> // Dtt=t*Dt+1 ==> // Dxx=x*Dx+1 ==> // Dyy=y*Dy+1 ```