Hidden Inversions (Cops' Thread)
Python 3, 80 bytes (Cracked)

bhmq = int(input())
print(bhmq ** 2)
(1 or [(sqrt),(specification+of*integerr)])


Domain: positive integers. Function is just squaring of a number. Input to stdin, output to stdout, as well as in the inverse function. Note that Python ignores the third line here, because it is syntactically valid and 1 is already a truthy value, so Python doesn't even look whether the right part of 'or' is well-defined.

Robbers should write a sqrt function that will work correct on all non-zero squares, printing integer value as is, without floating point (so on input '4' output should be '2' or '2\n', not '2.0' or '2.0\n').