let cyclefun = fun(r1: region) halfSegments(r1) 
                   filter[.Ldp] 
                   sortby[FaceNo, CycleNo, EdgeNo] 
                   projectextend[FaceNo, CycleNo, EdgeNo; B : boundary(.Segment)]  
                   projectextend[FaceNo, CycleNo, EdgeNo; PL : get(.B,0), PR : get(.B, 1) ]  
                   extend_last[RS : (.PR = ..PL) or (.PR = ..PR) :: FALSE] 
                   extend_next[RF : ifthenelse(.EdgeNo=0, (.PL = ..PL) or (.PL = ..PR), FALSE):: FALSE]
                   replaceAttr[RS : .RS or .RF] 
                   projectextend[FaceNo, CycleNo, EdgeNo; P1 : ifthenelse(.RS,.PR,.PL) , 
                                                          P2 : ifthenelse(not(.RS),.PR,.PL)
                   ] 

#
# This function returns the segments of a region ordered in a cyclic way.
# The last point of a segment is equals  the first point of the next segemnt.
# It works as follows:
# First, the halfsegments of a region are returned with additional information as
# FaceNo, CycleNo and EdgeNo. Only a single segment is used. We use only the 
# halfsegment that has a left dominating point.
# After that, we extract the both end points of each segment. 
# Now, we have to check whether the points must be swapped. This is the case if the 
# previous 'segment' has an endpoint equals to the second point of the current segment.
# A special treatment for the first segment is done. We swap its end points if the next (the second)
# segment has a point equals to the first point of this segment. 
#