This function finds the hash value for key in hash-table. If there is no entry for key in hash-table, default is returned (which in turn defaults to
nil).
This function removes the entry for key from hash-table. Does nothing if there is no entry for key in hash-table.
This function maps function over entries in hash-table, calling it with two args, each key and value in the hash table.
function may not modify hash-table, with the one exception that function may remhash or puthash the entry currently being processed by function.