reserve V for RealLinearSpace;
reserve p,q,u,v,w,y for VECTOR of V;
reserve a,b,c,d for Real;

theorem Th16:
  y=(v+w)-u implies u,v // w,y & u,w // v,y
proof
  set y=(v+w)-u;
  y+u=v+w by RLSUB_2:61;
  then y-v=w-u & y-w=v-u by Th2;
  hence thesis by Th15;
end;
