              P is the phase angle of pseudorotation for five membered rings. \
               This formulation is used for ribo and deoxyribo sugars in nucleic\
               acids.\
                          (tau4 +tau1)-(tau3+tau0)\
               P = ATAN (-------------------------)\
                           2tau2 (sin 36+sin 72)\
\
               If tau2 is <0, then P=P+180\
\
               This formulation is by Altona and Sundaralingam (1972), J.A.C.S.,\
               94, 8205-8212.