theorem Th22:
  p=u & q=v & p1=u1 & q1=v1 implies (p,q // p1,q1 iff ex a,b st a*
  (v-u) = b*(v1-u1) & (a<>0 or b<>0) )
proof
  assume
A1: p=u & q=v & p1=u1 & q1=v1;
  hereby
    assume p,q // p1,q1;
    then [[p,q],[p1,q1]] in the CONGR of AMSpace(V,w,y) by ANALOAF:def 2;
    hence ex a,b st a*(v-u) = b*(v1-u1) & (a<>0 or b<>0) by A1,Th15;
  end;
  given a,b such that
A2: a*(v-u) = b*(v1-u1) &( a<>0 or b<>0);
  [[u,v],[u1,v1]] in lambda(DirPar(V)) by A2,Th15;
  hence thesis by A1,ANALOAF:def 2;
end;
