theorem Th25:
  1 in C & (for A st A in dom fi holds fi.A = exp(C,A)) implies fi
  is increasing
proof
  assume that
A1: 1 in C and
A2: for A st A in dom fi holds fi.A = exp(C,A);
  let A,B;
  assume that
A3: A in B and
A4: B in dom fi;
A5: fi.B = exp(C,B) by A2,A4;
  fi.A = exp(C,A) by A2,A3,A4,ORDINAL1:10;
  hence thesis by A1,A3,A5,Th24;
end;
