def SUBTRACT(x, y):
return {'<STR_LIT>': [x, y]}<EOL>
Subtracts two numbers to return the difference,
or two dates to return the difference in milliseconds,
or a date and a number in milliseconds to return the resulting date.
See https://docs.mongodb.com/manual/reference/operator/aggregation/subtract/
for more details
:param x: The number or field of number
:param y: The number or field of number (is subtracted from the first argument)
:return: Aggregation operator