function [A] = lubpr(A)
A(2:end, 1) = A(2:end, 1) / A(1)
A(2:end, 2:end) = A(2:end, 2:end) - A(2:end, 1)*A(1, 2:end)
if (length(A) > 2)
  A(2:end, 2:end) = lubpr(A(2:end, 2:end))
end
end
