reserve AS for AffinSpace;
reserve A,K,M,X,Y,Z,X9,Y9 for Subset of AS;
reserve zz for Element of AS;
reserve x,y for set;

theorem Th22:
  x is Element of the Points of ProjHorizon(AS) implies x is POINT
  of IncProjSp_of(AS)
proof
  assume x is Element of the Points of ProjHorizon(AS);
  then ex X st x=LDir(X) & X is being_line by Th14;
  hence thesis by Th20;
end;
