       10 // IMPORT test program
       20 //
       30 a:=4
       40 b:=4
       50 aap
       60 SYS assert, a=6 AND b=100
       70 //
       80 PRINT "Ok"
       90 //
      100 PROC aap CLOSED
      110   IMPORT a
      120   SYS assert, a=4
      130   a:=6
      140   b:=7
      150   SYS assert, a=6 AND b=7
      160   olifant
      170 ENDPROC aap
      180 //
      190 PROC olifant CLOSED
      200   IMPORT aap: b
      210   SYS assert, b=7
      220   b:=9
      230   tijger
      240 ENDPROC olifant
      250 //
      260 PROC tijger CLOSED
      270   IMPORT _program: b
      280   b:=100
      290 ENDPROC tijger
