Returns true if the two xs:gYearMonth values have the same starting
            instant.
xs:gYearMonth values. Also
         used in the definition of the "ne" operator.op:gYearMonth-equal( $arg1 as xs:gYearMonth,$arg2 as xs:gYearMonthxs:booleanThe starting instants of $arg1 and $arg2 are calculated by
            supplying the missing components of $arg1 and $arg2 from the
               xs:dateTime template xxxx-xx-01T00:00:00. The function
            returns the result of comparing these two starting instants using
               op:dateTime-equal.
Assume that the dynamic context provides an implicit timezone value of
                  -05:00.
					op:gYearMonth-equal(xs:gYearMonth("1986-02"), xs:gYearMonth("1986-03"))
               returns false(). The starting instants are
                  1986-02-01T00:00:00-05:00 and 1986-03-01T00:00:00,
               respectively.
					op:gYearMonth-equal(xs:gYearMonth("1978-03"), xs:gYearMonth("1986-03Z"))
               returns false(). The starting instants are
                  1978-03-01T00:00:00-05:00 and 1986-03-01T00:00:00Z,
               respectively.