Rechnen in `QQ`


`(-1/2)*(1/3)` `(1/7)*(-1/3)` `(-1/2)*(-1/7)` `(-1/7)*(-1/13)`
`(-1/2)+(1/3)` `(-1/2)-(+1/3)` `(1/2)-(1/3)` `(1/2)+(1/3)`
`3/2*2.5-2.0` `2.5*2/5-1/5` `2.5*(2/5-1/5)` `(2.5*2/5)-1/5`
`49/64:7/8` `49/64:7` `64/49:64/49` `6.4/4.9:64/49`
`1/9` `1/3` `1/6` `1/8`
`0.bar 1 + 0.bar 2` `-0.bar 9 - 0.bar 9` `-0.bar 3 *3` `0.1bar 6 *(-3)`