Be aware that this a longish journey. Acquiring selectively mathematical skills at college level is complicated by the fact that there is quite a lot of interd

Be aware that this a longish journey. Acquiring selectively mathematical skills at college level is complicated by the fact that there is quite a lot of interdependency between subjects. This goes beyond proofs. You'll be stymied by notation and assumed background knowledge. College curricula obviously solve this somehow, so check a few of them out, and work backwards from your target subjects (eg graph theory) to find all the prerequisites.