Constant‐sign solutions for singular systems of Fredholm integral equations

We consider the system of Fredholm integral equations u i (t)= ∫ T 0 g i (t,s)[H i (s, u 1 (s), u 2 (s),...,u n (s))+K i (s, u 1 (s), u 2 (s),...,u n (s))]ds, t∈[0, T], 1≤i≤n where T>0 is fixed and the nonlinearities H i (t, u 1 , u 2 ,..., u n ) can be singular at t=0 and u j =0 where j ∈{1, 2,..., n}. Criteria are offered for the existence of constant-sign solutions, i.e. θ i u i (t)≥0 for t∈[0, 1] and 1 ≤i≤n, where θ i ∈{1, ―1} is fixed. We also include an example to illustrate the usefulness of the results obtained.