
theorem Th17: :: AChain1:
for R being RelStr, A being finite StableSet of R, n being Nat
  st n <= card A ex B being finite StableSet of R st card B = n
proof
 let R be RelStr, A be finite StableSet of R, n be Nat such that
A1: n <= card A;
   consider BB being finite Subset of A such that
A2: card BB = n by A1,FINSEQ_4:72;
   reconsider BB as finite StableSet of R by Th16;
   take BB;
   thus card BB = n by A2;
end;
