What does 1+1≠0 mean? I am using Schaum's outline of linear algebra in which there is a result that  the notion of alternating and skew-symmetric bilinear forms is equivalent provided that 1+1≠0, i.e a bilinear form f satisfying:
f(v,v)=0 satisfies f(u,v)=-f(v,u) and 
f(u,v)=-f(v,u) satisfies f(v,v)=0 
provided that 1+1≠0
I am confused with this sentence "1+1≠0"
Can anybody tell me what does it mean?
Thanks in advance

If you are working over the field $\mathbb F_2$, then you'll have $1+1=0$. More generally, the fields for which this equality holds are called fields with characteristic $2$. So, that book assumes that we are not working over such a field.
