function U(l,m,n,R_1,R_lm1) {
    
    return P(0,l,m,n,R_1,R_lm1);
}
function U(l,m,n,R_1,R_lm1) {
    
    return P(0,l,m,n,R_1,R_lm1);
}
function U ( l , m , n , R_1 , R_lm1 ) { return P ( 0 , l , m , n , R_1 , R_lm1 ) ; }
functions to compute terms U, V, W of Eq.8.1 (Table II)
functions to compute terms U V W of Eq . 8 . 1 ( Table II )