(1) subst(t,x+y,y+c+x) gives y+x+c, not t+c. On the
other hand, subst(u,x+y,y+x) does give u.
(2) subst(x,y^2,y^4+y^2) gives y^4+x instead of x^2+x.
(3) radcan(sqrt(1-y^6)/sqrt(1-y^2)); gives instead of
sqrt(y^4+y^2+1) a correct but complicated expression
-%i*sqrt(-y^2+y-1)*sqrt(y^2+y+1).
How could I get the desired form of the results?
Thanks in advance.
M. K. Shen