reserve a,b,c,d for Real;
reserve r,s for Real;

theorem Th81:
  0 < b & a*b < c implies a < c/b
proof
  assume that
A1: b>0 and
A2: a*b<c;
  a*b/b<c/b by A1,A2,Lm26;
  hence thesis by A1,XCMPLX_1:89;
end;
