MR-474 / 894b. problem

Simplify the fraction below::

a4+1-2a21-a-a2+a3

a4+1-2a21-a-a2+a3=

a4-2a2+1a3-a2-a+1

=(a2-1)2a2(a-1)-1(a-1)

=a2-12a-1·a2-1

=a2-12a-1·a-1a+1

=a2-12a-1·a+1a-1

=a2-12a2-1a-1

=a2-1·a2-1a2-1a-1

=a2-1a-1

=a-1·a+1a-1

=a-1·a+1a-1

=a+1