Opencv problem with ubuntu 18.04 (Solved)

Hi all!
I’m writing this post just to keep track of a problem i’ve encountered compiling just various example apps with openCv, failing with “No package ‘opencv’ found”.
After a little investigation i’ve found that “libopencv-dev” was not installed, even i’m pretty sure i’ve run the script.
If someone can investigate or just encounter the very same problem, this one should be the solution