odd bug in integrate: using x(t) instead of x get answer

Substituting x --> z[0] also shows this bug. Also

  (%i1) s:  1/sqrt(log(x)+a*x+b)$

  (%i2) integrate(subst(x=z[0],s),z[0]);
  (%o2) -sqrt(%pi)*%i*%e^(-b-z[0]*a)*erf(%i*sqrt(b+z[0]*a+log(z[0])))

  (%i3) integrate(subst(x=a+b,s),a+b);
  (%o3) a/sqrt(log(b+a)+(a+1)*b+a^2)

  (%i4) integrate(subst(x=%i,s),%i);
  Maxima encountered a Lisp error:

  (%i5) integrate(subst(x=sqrt(5),s),sqrt(5));
  (%o5) (2*sqrt(b+sqrt(5)*a+log(5)/2))/a

--Barton

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Interesting.  I haven't looked at what maxima does when integrating u,
but the answer doesn't appear correct, based on a plot with some
random values for a and b.

Ray

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