ABSTRACT
In this section we will prove some criteria for multiple periodic solutions for a class of first order ODEs. Let ω > 0 be arbitrarily chosen. For a continuous ω-periodic function a we denote [ a ] = 1 ω ∫ 0 ω a ( τ ) d τ . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003028727/1d426271-33df-4258-80cb-5188d2ed19c2/content/umath2_1.jpg"/> We will start with the following useful lemma.
