theorem Th70:
  for F being Function of [:D,D9:],E for p being FinSequence of D
for q being FinSequence of D9 st len p = len q & r = F.:(p,q) holds len r = len
  p & len r = len q
proof
  let F be Function of [:D,D9:],E;
  let p be FinSequence of D;
  let q be FinSequence of D9;
  assume that
A1: len p = len q and
A2: r = F.:(p,q);
  len r = min(len p,len q) by A2,Th69;
  hence thesis by A1;
end;
