theorem Th34:
  B <> {} & f|B = g|B implies FinJoin(B,f) = FinJoin(B,g)
proof
  assume that
A1: B <> {} and
A2: f|B = g|B;
  f.:B = g.:B by A2,RELAT_1:166;
  hence thesis by A1,SETWISEO:26;
end;
