Degree theory And phrases 2 Blood 2 Continuum mechanics 2 Differential equations 2 Global attractor 2 Hematopoiesis 2 Indefinite singularity 2 Landesman-Lazer condition 2 Landesman-Lazer conditions 2 Leray-Schauder continuation theorem 2 Multiplicity 2 Nonlinear beam equation 2 Nonlinear equations 2 Nonlinear nonautonomous delay differential equations 2 Ordinary differential equations 2 Periodic solutions 2 Positive periodic solution 2 Positive periodic solutions 2 Problem solving 2 Singular differential equations 2 Symmetric solution 2 Symmetric solutions 2 Topology 2 Variational methods 2