https://blog.csdn.net/a_forever_dream/article/details/83654397 (see definition)
https://www.cnblogs.com/ljh2000-jump/p/5869991.html (may assist reading)
topic:
Bare-based linear problems: https://www.luogu.org/problemnew/show/P3812 (Los Valley)
Linear-based practice:
https://www.luogu.org/problemnew/show/P4570 (Los Valley)
https://www.luogu.org/problemnew/show/P3292 (Los Valley)
https://www.luogu.org/problemnew/show/P3857 (Los Valley)
http://codeforces.com/problemset/problem/724/G（CF）