TY JOUR TI LEFT-INVARIANT ALMOST PARA-COMPLEX EINSTEINIAN STRUCTURES ON SIX-DIMENSIONAL NILPOTENT LIE GROUPS KW Nilmanifolds KW six-dimensional nilpotent Lie algebras left-invariant para-complex structures KW Einstein manifolds KW half-flat structures JO Science Evolution AU Smolentsev, N.K. PY 2017 IS 2 PB Kemerovo State University