[Definition 18.3, F]

Definition 42.22.1. Let $(S, \delta )$ be as in Situation 42.7.1. Let $X$ be a scheme locally of finite type over $S$. An envelope is a proper morphism $f : Y \to X$ which is completely decomposed (More on Morphisms, Definition 37.76.1).

In your comment you can use Markdown and LaTeX style mathematics (enclose it like $\pi$). A preview option is available if you wish to see how it works out (just click on the eye in the toolbar).