In numerous nonlinear phenomena the occurrence of isolas or closed isolated loops of solutions have been observed [1,3,5,8,11]. Theoretically such phenomena are described by the solutions of nonlinear eigenvalue problems which depend on two (or more) parameters. For example the equilibrium state u of some process is the solution of () G ( u,   λ, τ ) = 0 https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780203745465/59a6af57-aaec-4c6e-b5c4-3edadfc8e8fa/content/eq256.tif"/>