  In this paper we study the existence of solutions for nonlinear boundary
value problems ({\phi}(u' ))' = f(t,u,u'), l(u,u')=0 where l(u,u') =0 denotes
the Dirichlet or mixed conditions on [0, T], {\phi} is a bounded, singular or
classic homeomorphism such that {\phi}(0)=0, f(t,x,y) is a continuous function,
and T a positive real number. All the contemplated boundary value problems are
reduced to finding a fixed point for one operator defined on a space of
functions, and Schauder fixed point theorem or Leray-Schauder degree are used.
