buglist bug 7265: interpreter does early retract to Taylor series

Z ==> Integer
Q ==> Fraction Z
z:Symbol := 'z
L ==> UnivariateLaurentSeries(Q,z,0)
q:L := z::Variable(z)::L
t1:L := (1/((1-q)*(1-q^2)))
t2 := t1-1
recip t2
t3 := recip t2
t4:Union(L,"failed") := recip t2  -- bug in interpreter
t5:Union(L,"failed") := (recip t2)$L
t6:Union(L,"failed") := t3