https://swang87.r-universe.dev/fchttps://swang87.r-universe.dev/api/packages/fchttps://swang87.r-universe.dev/fc/fc.pdfhttps://swang87.r-universe.dev/fc/doc/manual.htmlhttps://swang87.r-universe.dev/fc/citationhttps://swang87.r-universe.dev/fc/citation.txthttps://swang87.r-universe.dev/fc/citation.cff