我05年2月开始还贷款的每月还820多，贷了12万，20年，现在想提前还一部分贷款，想请问怎么样还比较划算？

(3)
?p∈POsub,l∈LIsub:?(p in l);
(4)
?l∈LIsub,s∈PLsub:when ?(l in s) ∧have intersection,(intersection of l and s) ∈ POsub;
(5)
?l∈LIsub,v∈SOsub:when ?(l in v) ∧have intersection,(intersection of l and v) ∈ POsub;
(6)
?s∈PLsub,v∈SOsub:when ?(s in v) ∧have intersection,(intersection of s and v) ∈ POsub∪ LIsub;
(7)
?l1,l2∈LIsub:?(l1=l2)∧?(l1 and l2 intersect) ∧?(l1 and l2 overlap);
(8)
?s1,s2∈PLsub:?(s1=s2)∧?(s1 and s2 intersect) ∧?(s1 and s2 overlap);
(9)
?v1,v2∈SOsub:?(v1=v2)∧?(v1 and v2 meet in plane) ∧?(v1 and v2 overlap);
Intuitively, a RO is a set that composed of RPOs. Its points locate in grid points of RSDD. The two ends of its
lines also locate in RSDD and there are no other RPO-points on the lines except ends. For the relation of RPO-lines
and PRO-planes, either there is no intersection or their intersection is a RPO-point. For the relation of RPO-lines
and PRO-solids, either there is no inte