Concept history

Added exercise "De simples images réciproque"

Concept created

Let $f:X \rightarrow Y$ be a [[Map|map]] and $A\subseteq X$. The preimage of $A$ under $f$ is the [[Subset|subset]] of $X$ defined as:
$$f^{-1}(A)=\{x\in X:f(x)\in A\}.$$