- Explain why it is necessary to prove both ``if
*TeX Embedding failed!*then*TeX Embedding failed!*" and ``if*TeX Embedding failed!*then*TeX Embedding failed!*" in order to prove ``*TeX Embedding failed!*if and only if*TeX Embedding failed!*".In order to prove ``

*TeX Embedding failed!*if and only if*TeX Embedding failed!*" (aka ``*TeX Embedding failed!*iff*TeX Embedding failed!*") one must prove both ``if*TeX Embedding failed!*then*TeX Embedding failed!*" and ``if*TeX Embedding failed!*then*TeX Embedding failed!*". But why both? The necessity of ``if*TeX Embedding failed!*then*TeX Embedding failed!*" is obvious from the statement of the question and corresponds to the ``if" part. The ``only if" part refers to the notion that*TeX Embedding failed!*is true only when*TeX Embedding failed!*is**true**, i.e that*TeX Embedding failed!*is not true when*TeX Embedding failed!*is**false**, this is proven by showing that whenever*TeX Embedding failed!*is true,*TeX Embedding failed!*is also true and hence that*TeX Embedding failed!*is never false when*TeX Embedding failed!*is true, hence the expression ``only if".