<pre>
-for all `s1`, `s2`, `s3` in `S`:
-(i) `s1*s2` etc are also in `S`
-(ii) `(s1*s2)*s3` = `s1*(s2*s3)`
-(iii) `z*s1` = `s1` = `s1*z`
+ for all s1, s2, s3 in S:
+ (i) s1*s2 etc are also in S
+ (ii) (s1*s2)*s3 = s1*(s2*s3)
+ (iii) z*s1 = s1 = s1*z
</pre>
Some examples of monoids are: