  If one begins with the assertion that the type IIA string compactified on a
K3 surface is equivalent to the heterotic string on a four-torus one may try to
find a statement about duality in ten dimensions by decompactifying the
four-torus. Such a decompactification renders the K3 surface highly singular.
The resultant K3 surface may be analyzed in two quite different ways - one of
which is natural from the point of view of differential geometry and the other
from the point of view of algebraic geometry. We see how the former leads to a
"squashed K3 surface" and reproduces the Horava-Witten picture of the heterotic
string in M-theory. The latter produces a "stable degeneration" and is tied
more closely to F-theory. We use the relationship between these degenerations
to obtain the M-theory picture of a point-like E8-instanton directly from the
F-theory picture of the same object.
