In addition to the four old program units: PROGRAM (that is the main program), SUBROUTINE, FUNCTION and BLOCK DATA , the new concept MODULE has been added, as well as some new things in the old units. ... POSITIVE NUMBERS ASSUMED TYPE(INTERVAL), INTENT(IN) :: A, B TYPE (INTERVAL) :: INTERVAL_MULTIPLICATION INTERVAL_MULTIPLICATION%LOWER = A%LOWER * B%LOWER INTERVAL_MULTIPLICATION%UPPER = A%UPPER * B%UPPER END FUNCTION INTERVAL_MULTIPLICATION FUNCTION INTERVAL_DIVISION(A, B) ! ...