https://cloud.r-project.org/web/packages/formulops/index.html
CRAN: Package formulops
Perform mathematical operations on R formula (add, subtract, multiply, etc.) and substitute parts of formula.
cranpackage
https://www.r-project.org/nosvn/R.check/r-devel-linux-x86_64-debian-gcc/formulops-00check.html
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