((m-n+1)^2 - (m-1+n)^2/4mn) * (n+1)
((m-n+1)^2 - (m-1+n)^2/4mn) * (n+1)=
=((m-n+1)(m-n+1)- mn√(m-1+n))=
=m²-mn+m-mn+n²-n+m-n+1-mn√(m-1+n)=
=m²-2mn+2m+n²-2n+1-mn√(m-1+n)=? (not finished)