===

x === y -- returns true or false depending on whether the expressions x and y are strictly equal.

Strictly equal expressions have the same type, so

               0===0.

and

               0===0/1

are false: the three types involved here are ZZ, RR, and QQ.

If x and y are mutable then they are strictly equal only if they are identical (i.e., at the same address in memory). For details about why strict equality cannot depend on the contents of mutable hash tables, see hashing. On the other hand, if x and y are non-mutable, then they are strictly equal if and only if their contents are equal.