reserve X for set;
reserve CS for non empty CollStr;
reserve a,b,c for Point of CS;
reserve CLSP for CollSp;
reserve a,b,c,d,p,q,r for Point of CLSP;

theorem Th3:
  a<>b & a,b,p are_collinear & a,b,q are_collinear & a,b,r
  are_collinear implies p,q,r are_collinear
by Def4;
