|  |  D.11.4.9 xchange Procedure from libraryfindifs.lib(see  findifs_lib).
 
Example:Usage:
xchange(w,a,b); w,a,b strings
Return:
string
Purpose:
exchanges substring 'a' with a substring 'b' in the string w
Note:
 |  | LIB "findifs.lib";
" EXAMPLE:"; 
==>  EXAMPLE:
ring r = (0,dt,dh,A),Tt,dp;
poly p = (Tt*dt+dh+1)^2+2*A;
string s = texpoly("",p);
s;
==> $dt^{2}\cdot Tt^{2}+(2dtdh+2dt)\cdot Tt+(dh^{2}+2dh+2A+1)$
string t = xchange(s,"dh","dt");
t;
==> $dh^{2}\cdot Tt^{2}+(2dhdt+2dh)\cdot Tt+(dt^{2}+2dt+2A+1)$
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