I enjoy math, but when i have to proof something - i find it confucing. I dont know how strict proof should be. If proof ends with 17<18 , it this really end? Why shouldn't i proof that 17<18 is actually true? I never know what sentences can i treat as obvious, and which one i have to proof. This is same about proofs i find in books - there are conclusions that are treaten as obvious and not being proved. And i dont know when i can assume something is obvious. i could use some tips, or book suggestions. Description of my problem may be confusing, but i think is common and i will be understood. if not, i shall provide some examples.