The Absolute extrema (c, f(c)) in interval I of a function f.

1. If and only if (IFF) $f(c)\ge f(x)$for all x in I → absolute/global maximum.

   1. This is pretty intuitive, a absolute max must be greater than (not less than) the others to be the greatest.
   2. So there might be multiple absolute maximums in the function f.

2. If and only if (IFF) $f(c)\le f(x)$for all x in I → absolute/global minimum.

   1. This is pretty intuitive, a absolute min must be less than (not greater than) the others to be the least.
   2. So there might be multiple absolute minimums in the function f.

   All is min or max for a horizontal line