Multiplication of one two-site operator and one one-site operator (acting on one of the sites of the former) giving a new two-site operator.
The two-site operator a
is applied first to the physical state.
References syten::IPEPSv2::ATwoOp::assert_correctness(), syten::IPEPSv2::ATwoOp::left, syten::IdentityDenseTensorImpl::merge(), syten::IPEPSv2::ATwoOp::op, syten::STensorImpl::SBasisId::prime(), syten::project(), syten::IPEPSv2::ATwoOp::right, SYTEN_ASSERT, and syten::STensorImpl::STensor::unprime().