theorem
  F1 is affinely-independent & F2 is affinely-independent implies
     F1 \/ F2 is affinely-independent
 proof
  assume A1: F1 is affinely-independent & F2 is affinely-independent;
  let A;
  assume A in F1\/F2;
  then A in F1 or A in F2 by XBOOLE_0:def 3;
  hence thesis by A1;
 end;
