reserve p,q,r for FinSequence;
reserve u,v,x,y,y1,y2,z for object, A,D,X,Y for set;
reserve i,j,k,l,m,n for Nat;
reserve J for Nat;

theorem
  len p < len q iff dom p c< dom q
proof
A1: len p = len q iff dom p = dom q by Th27;
  len p <= len q iff dom p c= dom q by Th28;
  hence thesis by A1,XXREAL_0:1;
end;
