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

theorem Th84:
  b < 0 & c < a*b implies a < c/b
proof
  assume that
A1: b<0 and
A2: a*b>c;
  a*b/b<c/b by A1,A2,Lm29;
  hence thesis by A1,XCMPLX_1:89;
end;
