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The `#else' Directive

   The `#else' directive can be added to a conditional to provide
alternative text to be used if the condition is false.  This is what it
looks like:
     #if EXPRESSION
     TEXT-IF-TRUE
     #else /* Not EXPRESSION */
     TEXT-IF-FALSE
     #endif /* Not EXPRESSION */
   If EXPRESSION is nonzero, and thus the TEXT-IF-TRUE is active, then
`#else' acts like a failing conditional and the TEXT-IF-FALSE is
ignored.  Contrariwise, if the `#if' conditional fails, the
TEXT-IF-FALSE is considered included.