# op:same-key - XPath XQuery Reference

Determines whether two atomic values can coexist as separate keys within a map.deterministiccontext-independentfocus-independentThe internal function op:same-key (which is not available at the user level) is used to assess whether two atomic
            values are considered to be duplicates when used as keys in a map. A map cannot
         contain two separate entries whose keys are the same as defined by this function. 
         The function is also used when matching keys in functions such as map:get
         and map:remove.The function returns true if and only if one of the following conditions is true:All of the following conditions are true:$k1 is an instance of xs:string, xs:anyURI, or xs:untypedAtomic$k2 is an instance of xs:string, xs:anyURI, or xs:untypedAtomicfn:codepoint-equal($k1, $k2)Strings are compared without any dependency on collations.All of the following conditions are true:$k1 is an instance of xs:decimal, xs:double, or xs:float$k2 is an instance of xs:decimal, xs:double, or xs:floatOne of the following conditions is true:Both $k1 and $k2 are NaNxs:double('NaN') is the same key as xs:float('NaN')Both $k1 and $k2 are positive infinityxs:double('INF') is the same key as xs:float('INF')Both $k1 and $k2 are negative infinityxs:double('-INF') is the same key as xs:float('-INF')$k1 and $k2 when converted to decimal numbers with no rounding or loss of precision
                           are mathematically equal.Every instance of xs:double, xs:float, and xs:decimal can be represented
                              exactly as a decimal number provided enough digits are available both before and after the decimal point. Unlike the eq
                              relation, which converts both operands to xs:double values, possibly losing precision in the process, this
                              comparison is transitive.Positive and negative zero are the same key.All of the following conditions are true:$k1 is an instance of xs:date, xs:time, xs:dateTime,
                     xs:gYear, xs:gYearMonth, xs:gMonth, xs:gMonthDay, or xs:gDay$k2 is an instance of xs:date, xs:time, xs:dateTime,
                     xs:gYear, xs:gYearMonth, xs:gMonth, xs:gMonthDay, or xs:gDayOne of the following conditions is true:Both $k1 and $k2 have a timezoneNeither $k1 nor $k2 has a timezonefn:deep-equal($k1, $k2)The use of deep-equal rather than eq ensures that comparing values of different
                  types yields false rather than an error.Unlike the eq operator, this comparison has no dependency on the implicit timezone, which means that
                  the question of whether or not a map contains duplicate keys is not dependent on this aspect of the dynamic context.All of the following conditions are true:$k1 is an instance of xs:boolean, xs:hexBinary, xs:base64Binary,
                     xs:duration, xs:QName, or xs:NOTATION$k2 is an instance of xs:boolean, xs:hexBinary, xs:base64Binary,
                     xs:duration, xs:QName, or xs:NOTATIONfn:deep-equal($k1, $k2)The use of deep-equal rather than eq ensures that comparing values of different
                        types yields false rather than an error.The rules for comparing keys in a map are chosen to ensure that the comparison is:Context-free: there is no dependency on the static or dynamic contextError-free: any two atomic values can be compared, and the result is either true or false, never an errorTransitive: if A is the same key as B, and B is the same key as C, 
               then A is the same key as C.As always, any algorithm that delivers the right result is acceptable. For example, when testing whether an xs:double
         value D is the same key as an xs:decimal value that has N significant digits, it is not
         necessary to know all the digits in the decimal expansion of D to establish the result: computing the first N+1 
            significant digits (or indeed, simply knowing that there are more than N significant digits) is sufficient.