1. On first-order discontinuous differential equations with nonlinear boundary conditions;Heikkilä;Nonlinear World,1996
2. On first-order discontinuous differential equations with functional boundary conditions;Heikkilä;Adv. in Nonlinear Dynamics,1997
3. On solvability of first-order discontinuous scalar differential equations;Carl;Nonlinear Times and Digest,1995
4. Extension of the method of upper and lower solutions for discontinuous differential equations;Heikkilä;Diff. Eqns. and Dyn. Syst.,1993
5. A unified theory for first-order discontinuous scalar differential equations