changes the basering to another (already defined) ring.
Example:
ring r1=0,(x,y),lp;
// the basering is r1
ring r2=32003,(a(1..8)),ds;
// the basering is r2
setring r1;
// the basering is again r1
nameof(basering);
→ r1
listvar();
→ // r2 [0] ring
→ // r1 [0] *ring
→ // LIB [0] string standard.lib
Use in procedures:
All changes of the basering by a definition of a new ring or a
setring command in a procedure are local to this procedure. Use
keepring to move a ring, which is local to a procedure, up by one
nesting level.