Extrapolation of the lettering found on a 1976 calender by Wim Crouwel.
I know this has already been done before, here is one that was done by Wilson Thomas. Who did a far more extensivey version that also includes extended Latin. Check his version out here: https://fontstruct.com/fontstructions/show/795855/kalendar_1976
Apart from a couple of glyphs that were done notably different and some other tiny differences in detais the two are pretty similar, but most certainly not copied.