The Stacks project

Definition 42.59.4. Let $(S, \delta )$ be as in Situation 42.7.1. Let $f : X \to Y$ be a local complete intersection morphism of schemes locally of finite type over $S$. We say the gysin map for $f$ exists if we can write $f = g \circ i$ with $g$ smooth and $i$ an immersion. In this case we define the gysin map $f^! = i^! \circ g^* \in A^*(X \to Y)$ as above.