!! +var+ +exec+ +string+
tit:leveldata
type:$type_both
alias:levelpoints
syntax:!leveldata size ``xsize,ysize'' ranges ``x1,x2,y1,y2'' function ``f(x,y)'' [levels ``l1,l2,...'']
mean:Computes coordinates of points on the level curve of ``f(x,y)'', at levels ``l1,l2,...''\
 (defaults to one level 0). <p>\
  The computation is made from ``(x1,y1)'' to ``(x2,y2)'', and points are computed as integer\
  positions in a picture with size ``xsize,ysize''. </p><p>\
  Order of the fields is not important. All the fields except levels are mandatory.\
  </p>
