Zulkardi, Prahmana, R.C.I. and Putri, R.I.I. 2025. In memory of Jan de Lange and Kees Hoogland: Honoring their legacy and contributions to mathematics education in Indonesia. Journal on Mathematics Education. 16, 2 (Jul. 2025), 753–762. DOI:https://doi.org/10.22342/jme.v16i2.pp753-762.