add todo item

Author: victorpoughon

doc.md

@@ -151,4 +151,5 @@ GitHub](https://github.com/sponsors/victorpoughon). Thank you ❤️
 
 * Implement the "true inverse" of the square root: `sqinv(X) = sqrt(X) U -sqrt(X)`
 * Split full precision mode into two controls: input interpretation and display precision
-* Add `ans` variable (result of previous entry)
+* Add `ans` variable (result of previous entry)
+* Add intersection operator or function