Here we investigate the pure ( 0 , 1 , … , r − 2 , r ) -interpolation problem on the zeros of ( 1 − x 2 ) P n ( α ) ( x ) = ( 1 − x 2 ) P n ( α , α ) ( x ) , - 1$"> α > − 1 , where P n ( α , α ) ( x ) is the Jacobi polynomial of degree n with β = α .