[Axiom-developer] [#136 cercion of power series] Crash with this patch

[unknown]

Changes 
http://page.axiom-developer.org/zope/mathaction/136CercionOfPowerSeries/diff
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This patch doesn't check the equality of the expansion points and the symbols 
for different power series.
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Example::

  a:=series(sin(x))
  b:=taylor(sin(x),x=2)
  a*b

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forwarded from http://page.axiom-developer.org/zope/mathaction/address@hidden