^hash.sub[hash_to_be_subtracted]
The method subtracts hash_to_be_subtracted from hash, deleting keys common for both hashes.
Example
$man[
$.name[Jack]
$.age[22]
$.sex[m]
]
$woman[
$.name[Mary]
$.age[20]
]
^man.sub[$woman]
As a result, hash $man will remain with single key $man.sex containing value m.