reserve AS for AffinSpace;
reserve a,b,c,d,a9,b9,c9,d9,p,q,r,x,y for Element of AS;
reserve A,C,K,M,N,P,Q,X,Y,Z for Subset of AS;

theorem Th28:
  X is being_plane & M is being_line & a in X & M c= X implies a*M c= X
proof
  assume that
A1: X is being_plane and
A2: M is being_line and
A3: a in X & M c= X;
  set N = a*M;
  a in N & M // N by A2,Def3;
  hence thesis by A1,A3,Th23;
end;
