"First and above all he was a logician. At least thirty-five years
of the half-century
or so of his existence had been devoted exclusively to proving that two
and two always equal four, except in unusual cases, where they equal three or
five, as the
Case may be." -- Jacques Futrelle, "The Problem of Cell
13"
Most mathematicians are familiar with -- or have at least seen
references in the
Literature to -- the equation 2 + 2 = 4. However, the less well
known equation 2 + 2
= 5 also have a rich, complex history behind it. Like any other complex
quantity, this
History has a real part and an imaginary part; we shall deal
exclusively with the latter here.