1.
Croft, T., Davison, R.: Foundation maths. Pearson, Harlow, England (2020).
2.
Elementary Algebra Textbook, http://mathrev.redwoods.edu/ElemAlgText/.
3.
Mathematics Enhancement Programme, http://www.cimt.org.uk/projects/mepres/alevel/alevel.htm.
4.
Underground Mathematics, https://undergroundmathematics.org/.