       10 // IMPORT test program
       20 //   
       30 a$:="main program"
       40 aap
       50 SYS assert, a$="modified in aap2"
       60 PRINT "Ok"
       70 //
       80 PROC aap CLOSED
       90   a$:="proc aap"
      100   SYS assert, a$="proc aap"
      110   aap1
      120   SYS assert, a$="modified in aap1"
      130   aap2
      140   //
      150   PROC aap1 CLOSED
      160     IMPORT a$
      170     SYS assert, a$="proc aap"
      180     a$:="modified in aap1"
      190   ENDPROC aap1
      200   //
      210   PROC aap2 CLOSED
      220     IMPORT _program: a$
      230     SYS assert, a$="main program"
      240     a$:="modified in aap2"
      250   ENDPROC aap2
      260   //
      270 ENDPROC aap
