alpha n xs j x = (1-2*(x-xs j)*sum[1/(xs j-xs k)|k<-filter (/=j) [0..n]])*(l n xs j x)^2::Double
alpha n xs j x = (1-2*(x-xs j)*sum[1/(xs j-xs k)|k<-filter (/=j) [0..n]])*(l n xs j x)^2::Double
alpha n xs j x = (1-2*(x-xs j)*sum[1/(xs j-xs k)|k<-filter (/=j) [0..n]])*(l n xs j x)^2::Double