https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vn6j/index.html
Program Units (FORTRAN 77 Language Reference)
program unitsfortranlanguagereference
https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2024-2/block-data-program-units-overview.html
Block Data Program Units Overview
block dataprogram unitsoverview