An short excerpt from the book Operating System Concepts with Java:
Concepts are presented using intuitive descriptions. Important theoretical results are covered, but formal proofs are omitted. The bibliographical notes at the end of each chapter contain pointers to research papers in which results were first presented and proved, as well as references to material for further reading. In place of proofs, figures and examples are used to suggest why we should expect the result in question to be true.
I don't understand that last sentence. Especially the part at the beginning: in place of proofs, figures and examples are used to suggest.