flap1           1
flap2           #<PROCEDURE>
flap3           #<PROCEDURE>
flap4           #<PROCEDURE>
(flap1)         (1), wat niet kan : 1 is geen procedure
(flap2)         0
(flap3)         1
(flap4)         #<PROCEDURE>
flap1           1
(flap3)         0
(flap2)         1