t/(2-2t+t^2)= 1/(2t-2)
arcctg (1-t)= -1/(1+(t-1)^2)

= (((1/(2t-2))-(-1/(1+(t-1)^2)))(t^2)-( t/(2-2t+t^2))-(arcctg (1-t))2t)/t^4=...