(p+q')(p.q'+p.r)(p'r'+q')
=( p'(q')' )'.{( (pr)'.(pq')' )'.( (p'r')'(q')' )'}
={(p'q)'.( (pr)'.(pq') )'} + (p'r')'q )'
=( p'q+(pr)'.(pq')' + (p'r')'q )'
=( p'q+ (p'+r')(p'+q)+(p+r)q )'
=(p'q +p'+ p'r'+qp'+qr'+pq+qr)'
=( p'(q+1) +p'r+ q(p'+p)+q(r'+r) )'
=(p'(1+r)+q+q)'
=(p'+q)'
=p.q'