Binary Operations
Groups
100

For all 

a,b,c \in S, a(bc) = (ab)c.

What is an associative binary operation?

100

A set equipped with an associative binary operation with an identity and inverses for every element.

What is a group?

200

This element satisfies  e*x = x = x*e for all elements  x 

What is the identity element?

300

For an element  x , this satisfies  xy = 1 = yx .

What is the inverse of x?