Starts two or more data elements in one program unit at the same
  storage location, thereby overlaying them in memory.  Statement
  format:

     EQUIVALENCE (nlist)[,(nlist)]...

     nlist  Is a list of variables, array elements, arrays,
            or character substring references, separated by
            commas.  You must specify at least two of these
            entities in each list.

  The elements named within each set of parentheses are given the
  same storage location.  The data elements do not have to be of the
  same type or length.  An equivalency begins with the first byte of
  each element.  When an array or substring element is equivalenced,
  the entire array or string is equivalenced in its normal linear
  storage.

  You cannot equivalence array or string elements in a manner that is
  inconsistent with their normal linear order.  You cannot
  equivalence elements of the same array or string.  You cannot
  equivalence two elements that are both in common areas.

  The following objects cannot be specified in EQUIVALENCE
  statements:

   o  A dummy argument

   o  An allocatable array

   o  A pointer

   o  An object of nonsequence derived type

   o  An object of sequence derived type containing a pointer in the
      structure

   o  A function, entry, or result name

   o  A named constant

   o  A structure component

   o  A subobject of any of the above objects

  You can identify a multidimensional array element by a single
  subscript.  The single subscript designates the absolute position
  of the element within the array.