theorem Th17:
  k<>0 implies (k divides l iff l/k is Integer)
proof
  assume
A1: k<>0;
  hence k divides l implies l/k is Integer by XCMPLX_1:89;
  assume l/k is Integer;
  then reconsider m=l/k as Integer;
  l=k*m by A1,XCMPLX_1:87;
  hence k divides l;
end;
