"Even the +, −, =, and x signs we take for granted only came into widespread use in the 17th century. Which means that the earlier algebraists we know of … all had expressed their equations mostly in ...

We determine the general solution of the functional equation $f(x + y) + f(x - y) = A(y)f(x)\quad (x, y \in G),$ where G is a 2-divisible abelian group, f is a vector ...