Option variable
zeta%pi
Default value: true
When zeta%pi is true, zeta returns an expression
proportional to %pi^n for even integer n.
Otherwise, zeta returns a noun form zeta (n)
for even integer n.
(%i1) zeta%pi: true$ (%i2) zeta (4); 4 %pi (%o2) ---- 90 (%i3) zeta%pi: false$ (%i4) zeta (4); (%o4) zeta(4)