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 subst(rat[,varn,ratn]*)

 psubst(rat[,var,rat]*)

:: Substitute ratn for varn in expression rat.
(n=1,2,....
Substitution will be done successively from left to right
if arguments are repeated.)
 return

rational expression
 rat,ratn

rational expression
 varn

indeterminate

Substitutes rational expressions for specified kernels in a rational
expression.

subst(rat,var1,rat1,var2,rat2,...)
has the same effect as
subst(subst(rat,var1,rat1),var2,rat2,...).

Note that repeated substitution is done from left to right successively.
You may get different result by changing the specification order.

Ordinary
subst() performs
substitution at all levels of a scalar algebraic expression creeping
into arguments of function forms recursively.
Function psubst() regards such a function form as an independent
indeterminate, and does not attempt to apply substitution to its
arguments. (The name comes after Partial SUBSTitution.)

Since Asir does not reduce common divisors of a rational expression
automatically, substitution of a rational expression to an expression
may cause unexpected increase of computation time.
Thus, it is often necessary to write a special function to meet the
individual problem so that the denominator and the numerator do not
become too large.

The same applies to substitution by rational numbers.
[0] subst(x^33*y*x^2+3*y^2*xy^3,y,2);
x^36*x^2+12*x8
[1] subst(@@,x,1);
27
[2] subst(x^33*y*x^2+3*y^2*xy^3,y,2,x,1);
27
[3] subst(x*y^3,x,y,y,x);
x^4
[4] subst(x*y^3,y,x,x,y);
y^4
[5] subst(x*y^3,x,t,y,x,t,y);
y*x^3
[6] subst(x*sin(x),x,t);
sint(t)*t
[7] psubst(x*sin(x),x,t);
sin(x)*t
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