The characteristic of a ring <i>R</i> is the least positive 
integer <i>n</i> such that <i>nx = 0</i> for all <i>x</i> in <i>R.</i>  
If no such <i>n</i> exists, we say that <i>R</i> has characteristic 0.
The characteristic of <i>R</i> is denoted char <i>R</i>.