reserve
  a for natural Number,
  k,l,m,n,k1,b,c,i for Nat,
  x,y,z,y1,y2 for object,
  X,Y for set,
  f,g for Function;
reserve p,q,r,s,t for FinSequence;
reserve D for set;

theorem
  for p,q being FinSequence st p c= q or dom p c= dom q holds len p <= len q
  proof let p,q be FinSequence;
   assume p c= q or dom p c= dom q;
   then dom p c= dom q by RELAT_1:11;
   then
A1: Segm card dom p c= Segm card dom q by CARD_1:11;
   card dom p = card p & card dom q = card q by CARD_1:62;
   hence thesis by A1,NAT_1:39;
  end;
