Function: characteristic
Section: conversions
C-Name: characteristic
Prototype: mG
Help: characteristic(x): characteristic of the base ring over which x is
 defined.
Doc:
 returns the characteristic of the base ring over which $x$ is defined (as
 defined by \typ{INTMOD} and \typ{FFELT} components). The function raises an
 exception if incompatible primes arise from \typ{FFELT} and \typ{PADIC}
 components.
 \bprog
 ? characteristic(Mod(1,24)*x + Mod(1,18)*y)
 %1 = 6
 @eprog
