I have difficulties understanding why exactly Maple finds the question difficult to answer. First attempt: assume(a>0); a:=sqrt(b^2); eval(a, b=2); (1/2) / 2\ a := \b / (1/2) 4 I suppose the problem is that after the assignment Maple forgets the assumption a>0(?). Is there a way to make _real_ assumptions on variables, which Maple will not forget and possibly warn me if I try to violate?